Ecovyst (ECVT) 10-K 1 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Feb. 25, 2019	Jun. 29, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	PQ Group Holdings Inc.
Entity Central Index Key	1,708,035
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		135,705,568
Entity Public Float			$ 711,130,212

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Sales	$ 1,608,154	$ 1,472,101	$ 1,064,177
Cost of goods sold	1,226,520	1,095,265	810,085
Gross profit	381,634	376,836	254,092
Selling, general and administrative expenses	168,628	146,723	110,252
Other operating expense, net (Note 9)	29,450	64,225	62,301
Operating income	183,556	165,888	81,539
Equity in net (income) loss from affiliated companies	(37,611)	(38,772)	2,612
Interest expense, net	113,723	179,044	140,315
Debt extinguishment costs (Note 16)	7,751	61,886	13,782
Other expense (income), net	11,077	24,364	(6,053)
Income (loss) before income taxes and noncontrolling interest	88,616	(60,634)	(69,117)
Provision (benefit) for income taxes	28,995	(119,197)	10,041
Net income (loss)	59,621	58,563	(79,158)
Less: Net income attributable to the noncontrolling interest	1,321	960	588
Net income (loss) attributable to PQ Group Holdings Inc.	$ 58,300	$ 57,603	$ (79,746)
Net income (loss) per share:
Basic income (loss) per share (usd per share)	$ 0.44	$ 0.52	$ (1.02)
Diluted income (loss) per share (usd per share)	$ 0.43	$ 0.52	$ (1.02)
Weighted average shares outstanding:
Basic (shares)	133,380,567	111,299,670	78,016,005
Diluted (shares)	134,684,931	111,669,037	78,016,005

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 59,621	$ 58,563	$ (79,158)
Other comprehensive income (loss), net of tax:
Pension and postretirement benefits	(7,958)	(101)	6,865
Net (loss) gain from hedging activities	(330)	(3,590)	4,557
Foreign currency translation	(35,056)	60,601	(66,834)
Total other comprehensive income (loss)	(43,344)	56,910	(55,412)
Comprehensive income (loss)	16,277	115,473	(134,570)
Less: Comprehensive income (loss) attributable to noncontrolling interests	1,392	(152)	(465)
Comprehensive income (loss) attributable to PQ Group Holdings Inc.	$ 14,885	$ 115,625	$ (134,105)

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
ASSETS
Cash and cash equivalents	$ 57,854	$ 66,195
Receivables, net	196,770	193,456
Inventories (Note 10)	264,748	262,388
Prepaid and other current assets	39,244	26,929
Total current assets	558,616	548,968
Investments in affiliated companies (Note 11)	468,211	469,276
Property, plant and equipment, net	1,208,979	1,230,384
Goodwill	1,254,929	1,305,956
Other intangible assets, net	728,436	786,144
Other long-term assets	108,254	74,727
Total assets	4,327,425	4,415,455
LIABILITIES
Notes payable and current maturities of long-term debt	7,237	45,166
Accounts payable	148,365	149,326
Accrued liabilities	100,009	93,917
Total current liabilities	255,611	288,409
Long-term debt, excluding current portion	2,106,720	2,185,320
Deferred income taxes	196,124	189,336
Other long-term liabilities	104,825	120,471
Total liabilities	2,663,280	2,783,536
Commitments and contingencies (Note 23)
EQUITY
Common stock ($0.01 par); authorized shares 450,000,000; issued shares 135,758,269 and 135,244,379 on December 31, 2018 and 2017, respectively; outstanding shares 135,592,045 and 135,244,379 on December 31, 2018 and 2017, respectively	1,358	1,352
Preferred stock ($0.01 par); authorized shares 50,000,000; no shares issued or outstanding on December 31, 2018 and 2017	0	0
Additional paid-in capital	1,674,703	1,655,114
Retained earnings (accumulated deficit)	25,523	(32,777)
Treasury stock, at cost; shares 166,224 and 0 on December 31, 2018 and 2017, respectively	(2,920)	0
Accumulated other comprehensive (loss) income	(39,104)	4,311
Total PQ Group Holdings Inc. equity	1,659,560	1,628,000
Noncontrolling interest	4,585	3,919
Total equity	1,664,145	1,631,919
Total liabilities and equity	$ 4,327,425	$ 4,415,455

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized (shares)	450,000,000	450,000,000
Common stock, shares issued (shares)	135,758,269	135,244,379
Common stock, shares outstanding (shares)	135,592,045	135,244,379
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (shares)	50,000,000	50,000,000
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Treasury stock (shares)	166,224	0

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Retained earnings (accumulated deficit)	Treasury stock, at cost	Accumulated other comprehensive income (loss)	Non-controlling interest
Beginning balance, value at Dec. 31, 2015	$ 235,293	$ 0	$ 245,279	$ (10,634)	$ 0	$ 648	$ 0
Beginning balance, shares at Dec. 31, 2015		22,683,077			0
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(79,158)			(79,746)			588
Business Combination, value	918,769	$ 73	912,127				6,569
Business Combination, shares		83,169,873
Stock repurchases, value	(2,540)				$ (2,540)
Stock repurchases, shares					(207,546)
Equity contribution, value	6,600	$ 0	6,486		$ 114
Equity contribution, shares		529,375			9,255
Other comprehensive income (loss)	(55,412)					(54,359)	(1,053)
Distributions to noncontrolling interests	(1,040)						(1,040)
Stock compensation expense	5,432		3,245		$ 2,187
Shares issued under equity incentive plan, net of forfeitures, shares		70,005			176,722
Ending balance, value at Dec. 31, 2016	1,027,944	$ 73	1,167,137		$ (239)	(53,711)	5,064
Ending balance, shares at Dec. 31, 2016		106,452,330
Increase (Decrease) in Stockholders' Equity
Net income (loss)	58,563			57,603			960
Stock split and conversion, value	0	$ 989	(1,228)		$ 239
Stock split and conversion, shares		(232,571)			232,534
Issuance of common stock - IPO, value	480,696	$ 290	480,406
Issuance of common stock - IPO, shares		29,000,000
Other comprehensive income (loss)	56,910					58,022	(1,112)
Distributions to noncontrolling interests	(993)						(993)
Stock compensation expense	8,799		8,799
Shares issued under equity incentive plan, net of forfeitures, value	0	$ 0	0		$ 0
Shares issued under equity incentive plan, net of forfeitures, shares		24,620			(211,015)
Ending balance, value at Dec. 31, 2017	1,631,919	$ 1,352	1,655,114		$ 0	4,311	3,919
Ending balance, shares at Dec. 31, 2017		135,244,379
Increase (Decrease) in Stockholders' Equity
Net income (loss)	59,621			58,300			1,321
Stock repurchases, value	(2,920)				$ (2,920)
Stock repurchases, shares					(166,224)
Other comprehensive income (loss)	(43,344)					(43,415)	71
Distributions to noncontrolling interests	(726)						(726)
Stock compensation expense	19,464		19,464
Shares issued under equity incentive plan, net of forfeitures, value	131	$ 6	125		$ 0
Shares issued under equity incentive plan, net of forfeitures, shares		513,890			0
Ending balance, value at Dec. 31, 2018	$ 1,664,145	$ 1,358	$ 1,674,703	$ 25,523	$ (2,920)	$ (39,104)	$ 4,585
Ending balance, shares at Dec. 31, 2018		135,758,269			(166,274)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income (loss)	$ 59,621	$ 58,563	$ (79,158)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation	132,640	124,551	89,453
Amortization	52,594	52,589	38,836
Amortization of inventory step-up	1,603	871	29,086
Intangible asset impairment charge	0	0	6,873
Amortization of deferred financing costs and original issue discount	6,119	8,733	6,859
Debt extinguishment costs	5,627	61,362	8,561
Foreign currency exchange loss (gain)	13,810	25,786	(3,558)
Pension and postretirement healthcare benefit expense	1,073	3,289	1,957
Pension and postretirement healthcare benefit funding	(7,602)	(7,887)	(2,887)
Deferred income tax provision (benefit)	3,445	(140,212)	(138)
Net loss on asset disposals	6,574	5,793	4,216
Stock compensation	19,464	8,799	5,432
Equity in net (income) loss from affiliated companies	(37,611)	(38,772)	2,612
Dividends received from affiliated companies	40,195	44,071	7,636
Net interest income on swaps designated as net investment hedges	(4,859)	0	0
Gain on contract termination	(20,612)	0	0
Other, net	(1,517)	(4,061)	(7,091)
Working capital changes that provided (used) cash, excluding the effect of business combinations:
Receivables	(10,451)	(11,463)	27,757
Inventories	(8,980)	(21,200)	(2,305)
Prepaids and other current assets	(6,348)	(3,434)	548
Accounts payable	(146)	4,343	11,885
Accrued liabilities	4,005	(6,548)	(23,866)
Net cash provided by operating activities	248,644	165,173	122,708
Cash flows from investing activities:
Purchases of property, plant and equipment	(131,688)	(140,482)	(121,421)
Investment in affiliated companies	(5,000)	(9,000)	0
Loan receivable under the New Markets Tax Credit Arrangement	0	(6,221)	(15,598)
Business combinations, net of cash acquired	(1,006)	(41,572)	(1,777,740)
Proceeds from sale of assets	12,380	0	0
Net interest proceeds on swaps designated as net investment hedges	4,859	0	0
Other, net	1,165	1,293	(1,004)
Net cash used in investing activities	(119,290)	(195,982)	(1,915,763)
Cash flows from financing activities:
Draw down of revolver	141,764	357,773	145,000
Repayments of revolver	(166,778)	(334,180)	(167,000)
Issuance of long-term debt, net of original issue discount and financing fees	1,267,000	308,550	1,248,556
Issuance of long-term notes, net of original issue discount and financing fees	0	0	1,133,265
Debt issuance costs	(6,395)	(4,666)	(23,786)
Repayments of long-term debt	(1,369,690)	(739,472)	(479,059)
Debt prepayment fees	0	(47,875)	0
IPO proceeds	0	507,500	0
IPO costs	0	(26,804)	0
Interest hedge premium	0	0	(1,551)
Equity contribution	0	0	6,600
Stock repurchases	(2,920)	0	(2,540)
Distributions to noncontrolling interests	(725)	(993)	(1,040)
Other	519	0	0
Net cash (used in) provided by financing activities	(137,225)	19,833	1,858,445
Effect of exchange rate changes on cash, cash equivalents and restricted cash	354	(6,858)	(5,886)
Net change in cash, cash equivalents and restricted cash	(7,517)	(17,834)	59,504
Cash, cash equivalents and restricted cash at beginning of period	67,243	85,077	25,573
Cash, cash equivalents and restricted cash at end of period	$ 59,726	$ 67,243	$ 85,077

Background and Basis of Present

Background and Basis of Presentation	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Background and Basis of Presentation	1. Background and Basis of Presentation: Description of Business PQ Group Holdings Inc. and subsidiaries (the “Company” or “PQ Group Holdings”) conducts operations through two reporting segments: (1) Environmental Catalysts and Services: a leading global innovator and producer of silica catalysts used in the production of high-density polyethylene (“HDPE”), methyl methacrylate (“MMA”), specialty zeolite-based catalysts sold to the emission control industry, the petrochemical industry and other areas of the broader chemicals industry and a merchant sulfuric acid producer operating a network of plants serving a variety of end uses, including the oil refining, nylon, mining, general industrial and chemical industries; and (2) Performance Materials and Chemicals: a fully integrated, global leader in silicate technology, producing sodium silicate, specialty silicas, zeolites, spray dry silicates, magnesium silicate, and other high performance chemical products used in a variety of end-uses such as adsorbents for surface coatings, clarifying agents for beverages, cleaning and personal care products and engineered glass products for use in highway safety, polymer additives, metal finishing and electronics end uses. Seasonal changes and weather conditions typically affect the Company’s performance materials and refining services product groups. In particular, the Company’s performance materials product group generally experiences lower sales and profit in the first and fourth quarters of the year because highway striping projects typically occur during warmer weather months. Additionally, the Company’s refining services product group typically experiences similar seasonal fluctuations as a result of higher demand for gasoline products in the summer months. As a result, working capital requirements tend to be higher in the first and fourth quarters of the year, which can adversely affect the Company’s liquidity and cash flows. Because of this seasonality associated with certain of the Company’s product groups, results for any one quarter are not necessarily indicative of the results that may be achieved for any other quarter or for the full year. Basis of Presentation PQ Merger with Eco Services On August 17, 2015, the Company, PQ Holdings Inc. (“PQ Holdings”), Eco Services Operations LLC (“Eco Services”), certain investment funds affiliated with CCMP Capital Advisors, LLC (now known as CCMP Capital Advisors, LP; “CCMP”), and stockholders of PQ Holdings and Eco Services entered into a reorganization and transaction agreement pursuant to which the companies consummated a series of transactions to reorganize and combine the businesses of PQ Holdings and Eco Services (the “Business Combination”), under a new holding company, PQ Group Holdings Inc. The Business Combination was consummated on May 4, 2016. In accordance with accounting principles generally accepted in the United States (“GAAP”), Eco Services is the accounting predecessor to PQ Group Holdings. Certain investment funds affiliated with CCMP held a controlling interest position in Eco Services prior to the Business Combination. In addition, certain investment funds affiliated with CCMP owned a non-controlling interest in PQ Holdings prior to the Business Combination and the merger with Eco Services constituted a change in control under the PQ Holdings credit agreements and bond indenture that were in place at the time of the Business Combination. Therefore, Eco Services is deemed to be the accounting acquirer. These consolidated financial statements are the continuation of Eco Services’ business prior to the Business Combination. Stock Split and Initial Public Offering Prior to September 22, 2017, the Company had two classes of common stock designated as Class A and Class B common stock. On September 22, 2017, the Company reclassified its Class A common stock into common stock and then effected a 8.8275 -for-1 split of its common stock. On September 28, 2017, the Company converted each outstanding share of Class B common stock into 8.8275 shares of common stock plus an additional number of shares determined by dividing the unreturned paid-in capital amount of such Class B common stock, or $113.74 per share, by $17.50 , the price of a share of common stock in the Company’s initial public offering (“IPO”), rounded to the nearest whole share. Holders of Class B common stock did not receive any cash payments from the Company in connection with the conversion of the Class B common stock. As a result of the reclassification of Class A common stock into common stock, and the conversion of Class B common stock into common stock, all references to “Class A common stock” and “Class B common stock” have been changed to “common stock” for all periods presented. All previously reported per share and common share amounts in the accompanying financial statements and related notes have been restated to reflect the stock split. On October 3, 2017, the Company completed its IPO whereby it issued 29,000,000 shares of its common stock at a price of $17.50 per share. The shares began trading on the New York Stock Exchange on September 29, 2017. The aggregate proceeds received by the Company from the offering were $480,696 , net of underwriting discounts, commissions and offering expenses. The net proceeds were used to repay existing indebtedness as further described in Note 16 .

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies: Principles of Consolidation. The consolidated financial statements include the accounts of the Company and its controlled subsidiaries. Investments in affiliated companies are recorded at cost plus the Company’s equity in their undistributed earnings. All intercompany transactions have been eliminated. Noncontrolling interests represent third-party equity ownership in certain of the Company’s consolidated subsidiaries and are presented as a component of equity separate from the equity attributable to the Company’s shareholders. The noncontrolling interests’ share in the Company’s net earnings are included in net income attributable to the noncontrolling interest in the Company’s consolidated statements of operations, and their portion of the Company’s comprehensive income is included in comprehensive loss attributable to noncontrolling interests in the Company’s consolidated statements of comprehensive income (loss). The Company’s noncontrolling interests relate to third-party minority ownership interests held in certain of the Company’s foreign subsidiaries acquired as part of the Business Combination. Foreign Currency Translation. All assets and liabilities of foreign subsidiaries and affiliated companies are translated to U.S. dollars using exchange rates in effect at the balance sheet date. Adjustments resulting from translation of the balance sheets and intercompany loans, which are considered permanent, are included in stockholders’ equity as part of accumulated other comprehensive income (loss). Adjustments resulting from translation of certain intercompany loans, which are not considered permanent and are denominated in foreign currencies, are included in other (income) expense, net in the consolidated statements of operations. The Company considers intercompany loans to be of a permanent or long-term nature if management expects and intends that the loans will not be repaid. For the years ended December 31, 2018 , 2017 and 2016 , all intercompany loan arrangements were determined to be non-permanent based on management’s intention as well as actual lending and repayment activity. Therefore, the foreign currency transaction gains or losses associated with the intercompany loans were recorded in the consolidated statements of operations for the years ended December 31, 2018 , 2017 and 2016 . Income and expense items are translated at average exchange rates during the year. Net foreign currency exchange (gains) and losses included in other expense (income), net were $13,810 , $25,786 and $(3,558) for the years ended December 31, 2018 , 2017 and 2016 , respectively. The net foreign currency losses realized in 2018 and 2017 and gain realized in 2016 were primarily driven by the Euro-denominated term loan (which was settled as part of the February 2018 term loan refinancing, see Note 16 to these consolidated financial statements for further information) and the non-permanent intercompany debt denominated in local currency and translated to U.S. dollars. Cash and Cash Equivalents. Cash and cash equivalents include investments with original terms to maturity of 90 days or less from the time of purchase. Restricted Cash. Restricted cash, which is restricted as to withdrawal or usage, is classified separately from cash and cash equivalents on our consolidated balance sheets. The proceeds from the New Markets Tax Credit (“NMTC”) financing arrangements are restricted for use and are classified on the Company’s consolidated balance sheets as other current assets. See Note 16 to these consolidated financial statements for further information regarding the NMTC financing arrangements. The Company’s total restricted cash balances, including cash related to the NMTC financing arrangements, were $1,872 and $1,048 as of December 31, 2018 and 2017 , respectively, and are included on the Company’s consolidated balance sheets as other current assets. Accounts Receivable and Allowance for Doubtful Accounts. Trade accounts receivable are recorded at the invoiced amount and do not bear interest. The allowance for doubtful accounts is the Company’s best estimate of the amount of probable credit losses in its existing accounts receivable. A specific reserve for bad debt is recorded for known or suspected doubtful accounts receivable. For all other accounts, the Company recognizes a reserve for bad debt based on the length of time receivables are past due and historical write-off experience. Account balances are charged against the allowance when the Company believes it is probable that the associated receivables will not be recovered. If the financial condition of the Company’s customers were to deteriorate resulting in an impairment of their ability to make payments, additional allowances may be required. The Company does not have any off-balance sheet credit exposure related to its customers. As of December 31, 2018 and 2017 , the Company’s allowance for doubtful accounts was not material. Inventories. Certain domestic inventories are stated at the lower of cost or market and valued using the last-in, first-out (“LIFO”) method. All other inventories are stated at the lower of cost and net realizable value and valued using the weighted average cost or first-in, first-out (“FIFO”) methods. Property, Plant and Equipment. Property, plant and equipment are carried at cost and include expenditures for new facilities, major renewals and betterments. The Company capitalizes the cost of furnace rebuilds as part of property, plant and equipment. Plant and equipment under capital leases are carried at the present value of minimum lease payments as determined at the beginning of the lease term. Maintenance, repairs and minor renewals are charged to expense as incurred. The Company capitalizes certain internal costs associated with the implementation of purchased software. When property, plant and equipment is retired or otherwise disposed of, the net carrying amount is eliminated with any gain or loss on disposition recognized in earnings at that time. The Company also leases property, plant and equipment, principally under operating leases. Rent expense for operating leases, which may have escalating rentals or rent holidays, is recorded on a straight-line basis over the respective lease terms. Depreciation is provided on the straight-line method based on the estimated useful lives of the assets, which generally range from 15 to 33 years for buildings and improvements and 3 to 10 years for machinery and equipment. Leasehold improvements are depreciated using the straight-line method based on the shorter of the useful life of the improvement or remaining lease term. The Company capitalizes the interest cost associated with the development and construction of significant new plant and equipment and depreciates that amount over the lives of the related assets. Capitalized interest recorded during the years ended December 31, 2018 , 2017 and 2016 was $3,542 , $5,806 and $5,687 , respectively. Spare Parts. Spare parts are maintained by the Company’s facilities to keep machinery and equipment in working order. Spare parts are capitalized and included in other long-term assets. Spare parts are measured at cost and are not depreciated or expensed until utilized; however, reserves may be provided on aged spare parts. When a spare part is utilized as part of an improvement to property, plant and equipment, the carrying value is depreciated over the applicable life once placed in service. Otherwise, the spare part is expensed and charged as a cost of production when utilized. Investments in Affiliated Companies. Investments in affiliated companies are accounted for using the equity method of accounting if the investment provides the Company with the ability to exercise significant influence, but not control, over the investee. Significant influence is generally deemed to exist if the Company’s ownership interest in the voting stock of the investee ranges between 20% and 50%, although other factors, such as representation on the investee’s board of directors and the impact of commercial arrangements, are considered in determining whether the equity method of accounting is appropriate. Under the equity method of accounting, the investments in equity-method investees are recorded in the consolidated balance sheets as investments in affiliated companies, and the Company’s share of the investees’ earnings or losses, together with other-than temporary impairments in value, is recorded as equity in net income (loss) from affiliated companies in the consolidated statements of operations. Any differences between the Company’s cost of an equity method investment and the underlying equity in the net assets of the investment, such as fair value step-ups resulting from acquisitions, are accounted for according to their nature and impact the amounts recognized as equity in net income (loss) from affiliated companies in the consolidated statements of operations. The Company evaluates all distributions received from its equity method investments using the nature of distribution approach. Under this approach, the Company evaluates the nature of activities of the investee that generated the distribution. The distributions received are either classified as a return on investment, which is presented as a component of operating activities on the Company’s consolidated statements of cash flows, or as a return of investment, which is presented as a component of investing activities on the Company’s consolidated statements of cash flows. The Company evaluates its equity method investments for impairment whenever events or changes in circumstances indicate that the carrying amounts of such investments may be impaired. If a decline in the value of an equity method investment is determined to be other than temporary, a loss is recorded in earnings in the current period. Goodwill and Intangible Assets. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. The Company is required to test goodwill associated with each of its reporting units for impairment at least annually and whenever events or circumstances indicate that it is more likely than not that goodwill may be impaired. The Company performs its annual goodwill impairment test as of October 1 of each year. Goodwill is tested for impairment at the reporting unit level. In performing tests for goodwill impairment, the Company is permitted to first perform a qualitative assessment about the likelihood of the carrying value of a reporting unit exceeding its fair value. If an entity determines that it is more likely than not that the fair value of a reporting unit is less than its carrying amount based on the qualitative assessment, it is required to perform a two-step goodwill impairment test to identify the potential goodwill impairment and measure the amount of the goodwill impairment loss, if any, to be recognized for that reporting unit. However, if an entity concludes otherwise based on the qualitative assessment, the two-step goodwill impairment test is not required. The option to perform the qualitative assessment can be utilized at the Company’s discretion, and the qualitative assessment need not be applied to all reporting units in a given goodwill impairment test. For an individual reporting unit, if the Company elects not to perform the qualitative assessment, or if the qualitative assessment indicates that it is more likely than not that the fair value of a reporting unit is less than its carrying amount, then the Company must perform the two-step goodwill impairment test for the reporting unit. In applying the two-step process, the first step used to identify potential impairment involves comparing the reporting unit’s estimated fair value to its carrying value, including goodwill. If the estimated fair value of a reporting unit exceeds its carrying value, goodwill is not impaired. If the carrying value exceeds the estimated fair value, there is an indication of potential impairment and the second step is performed to measure the amount of impairment, if any. The second step of the process involves the calculation of an implied fair value of goodwill for each reporting unit for which step one indicated potential impairment. The implied fair value of goodwill is determined in a manner similar to how goodwill is calculated in a business combination. That is, the estimated fair value of the reporting unit, as calculated in step one, is allocated to the individual assets and liabilities as if the reporting unit was being acquired in a business combination. If the implied fair value of goodwill exceeds the carrying value of goodwill assigned to the reporting unit, there is no impairment. If the carrying value of goodwill assigned to a reporting unit exceeds the implied fair value of the goodwill, an impairment charge is recorded to write down the carrying value. An impairment loss cannot exceed the carrying value of goodwill assigned to a reporting unit and the loss establishes a new basis in the goodwill. Subsequent reversal of an impairment loss is not permitted. For intangible assets other than goodwill, definite-lived intangible assets are amortized over their respective estimated useful lives. Intangible assets with indefinite lives are not amortized, but rather are tested for impairment at least annually or more frequently if events occur or circumstances change that would more likely than not reduce the fair value of the intangible asset below its carrying amount. The Company tests its indefinite-lived intangible assets as of October 1 of each year in conjunction with its annual goodwill impairment test. Impairment Assessment of Long-Lived Assets. The Company performs an impairment review of property, plant and equipment and definite-lived intangible assets when facts and circumstances indicate that the carrying value of an asset or asset group may not be recoverable from its undiscounted future cash flows. When evaluating long-lived assets for impairment, if the carrying amount of an asset or asset group is found not to be recoverable, a potential impairment loss may be recognized. An impairment loss is measured by comparing the carrying amount of the asset or asset group to its fair value. Fair value is determined using quoted market prices when available, or other techniques including discounted cash flows. The Company’s estimates of future cash flows involve assumptions concerning future operating performance, economic conditions and technological changes that may affect the future useful lives of the assets. Derivative Financial Instruments. The Company utilizes certain derivative financial instruments to enhance its ability to manage risk, including exposure to interest rate, commodity price, and foreign currency fluctuations that exist as part of ongoing business operations. Derivative instruments are entered into for periods consistent with the related underlying exposures and do not constitute positions independent of those exposures. All derivatives designated as hedges are recognized on the consolidated balance sheets at fair value. The Company may designate a derivative as a hedge of the fair value of a recognized asset or liability or of an unrecognized firm commitment (fair value hedge), a hedge of a forecasted transaction or the variability of cash flows to be received or paid related to a recognized asset or liability (cash flow hedge), a foreign currency fair-value or cash-flow hedge (foreign currency hedge), or a hedge of a net investment in a foreign operation (net investment hedge). The Company’s hedging strategies include derivatives designated as cash flow hedges and net investment hedges. Changes in the fair value of a derivative that is highly effective and that is designated and qualifies as a cash flow hedge are recorded in other comprehensive income and subsequently reclassified into earnings in the same period(s) in which the hedged transaction affects earnings. Changes in the fair value of a derivative that is highly effective and that is designated and qualifies as a hedge of a net investment in a foreign operation are recorded in the foreign currency translation adjustment account within accumulated other comprehensive income, where the associated gains and losses will remain until such time that the hedged net investment (foreign subsidiary) is sold or liquidated. Changes in the fair value of a derivative that is not designated or does not qualify as a hedge are recorded in the consolidated statements of operations. Cash flows from derivative instruments are reported in the same cash flow category as the cash flows from the items being hedged. The Company formally documents all relationships between hedging instruments and hedged items, as well as its risk-management objective and strategy for undertaking various hedge transactions. The Company also formally assesses whether each hedging relationship is highly effective in achieving offsetting changes in fair values or cash flows of the hedged item during the period, both at the inception of the hedge and on an ongoing basis. If it is determined that a derivative is not highly effective as a hedge, or if a derivative ceases to be a highly-effective hedge, hedge accounting is discontinued with respect to that derivative prospectively. Fair Value Measurements. The Company measures fair value using the guidelines under GAAP. An asset’s fair value is defined as the price at which the asset could be exchanged in a current transaction between market participants. A liability’s fair value is defined as the amount that would be paid to transfer the liability to a market participant, not the amount that would be paid to settle the liability with the creditor. See Note 5 to these consolidated financial statements regarding the application of fair value measurements. The carrying values of cash, accounts receivable, accounts payable and accrued liabilities approximate fair value due to the short-term nature of these items. See Note 16 to these consolidated financial statements regarding the fair value of debt. Revenue Recognition. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the contract with the customer; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company identifies a contract when an agreement with a customer creates legally enforceable rights and obligations, which occurs when a contract has been approved by both parties, the parties are committed to perform their respective obligations, each party’s rights and payment terms are clearly identified, commercial substance exists and it is probable that the Company will collect the consideration to which it is entitled. The Company may offer rebates to customers who have reached a specified volume of optional purchases. The Company recognizes rebates given to customers as a reduction of revenue based on an allocation of the cost of honoring rebates earned and claimed to each of the underlying revenue transactions that result in progress by the customer toward earning the rebate. Rebates are recognized at the time revenue is recorded. The Company measures the rebate obligation based on the estimated amount of sales that will result in a rebate at the adjusted sales price per the respective sales agreement. Shipping and Handling Costs. Amounts billed to a customer in a sale transaction related to shipping and handling, if any, represent revenues earned for the goods provided and are classified as revenue. Costs related to shipping and handling of products shipped to customers are classified as cost of goods sold. Refer to Note 4 for disclosures regarding the recognition of revenue for shipping and handling costs that are billed to customers. Research and Development. Research and development costs of $15,565 , $13,859 and $7,266 for the years ended December 31, 2018 , 2017 and 2016 , respectively, were expensed as incurred and reported in selling, general and administrative expenses in the consolidated statements of operations. Income Taxes. Prior to the Business Combination, Eco Services was a single member limited liability company and was treated as a partnership for federal and state tax purposes. All income tax liabilities and/or benefits of the Company were passed through to the member. As such, no recognition of federal or state income taxes for the Company have been provided for tax periods prior to the Business Combination. As a result of the Business Combination, Eco Services had a change in tax status and is taxed as a C-Corporation. The Company operates within multiple taxing jurisdictions and are subject to tax filing requirements and audit within these jurisdictions. The Company uses the asset and liability method in accounting for income taxes. Deferred tax assets and liabilities are recorded for temporary differences between the tax basis of assets and liabilities and their reported amounts in the financial statements, using statutory tax rates in effect for the year in which the differences are expected to reverse. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the results of operations in the period that includes the enactment date. The Company evaluates its deferred tax assets each period to ensure that estimated future taxable income will be sufficient in character (e.g., capital gain versus ordinary income treatment), amount and timing to result in their recovery. A valuation allowance is recorded to reduce the carrying amounts of deferred tax assets unless it is more likely than not that those assets will be realized. In determining the provision for income taxes, the Company provides deferred income taxes on income from foreign subsidiaries as such earnings are taxable upon remittance to the United States, to the extent that these earnings are considered to be available for repatriation. The Company does not provide income taxes on the cumulative unremitted earnings of foreign subsidiaries considered permanently reinvested. The Company establishes contingent liabilities for possible assessments by taxing authorities resulting from uncertain tax positions including, but not limited to, transfer pricing, deductibility of certain expenses and other state, local, and foreign tax matters. The Company recognizes a financial statement benefit for positions taken for tax return purposes when it will be more likely than not (greater than 50%) that the positions will be sustained upon tax examination, based solely on the technical merits of the tax positions, otherwise, no benefit is recognized. The tax benefits recognized are measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. The Company recognizes potential accrued interest and penalties related to unrecognized tax benefits in income tax expense. Tax examinations are often complex as tax authorities may disagree with the treatment of items reported by the Company and may require several years to resolve. These accrued liabilities represent a provision for taxes that are reasonably expected to be incurred on the basis of available information but which are not certain. Pursuant to the Securities and Exchange Commission (“SEC”) Staff Accounting Bulletin No.118 (“SAB 118”), the Company was allowed a measurement period of up to one year after the enactment date of the Tax Cuts and Jobs Act (“TCJA”) to finalize the recording of any related tax impacts with respect to its transition tax liability. As of December 31, 2017 , the Company’s accounting for these impacts was provisional. However, in accordance with SAB 118, the Company has finalized the impacts of the transition tax as of December 31, 2018 and has recorded a measurement period adjustment of $2,102 as a benefit to tax expense. There was no cash tax outlay associated with the final transition tax amount, as the Company elected to utilize net operating loss (“NOL”) carryforwards to offset the associated taxable income. Based on FASB guidance, the Company is permitted to make an accounting policy election to either (1) treat the taxes incurred as a result of the GILTI provision as a current-period expense when incurred or (2) factor such amounts into its measurement of deferred taxes. The Company has elected to treat any expense incurred as a current-period expense. Asset Retirement Obligations. The Company records a liability when the fair value of any future obligation to retire a long-lived asset as a result of an existing or enacted law, statute, ordinance or contract is reasonably estimable. The Company also records a liability for the fair value of a conditional asset retirement obligation if the fair value can be reasonably estimated. When the liability is initially recorded, the Company capitalizes the cost by increasing the amount of the related long-lived asset. Over time, the Company adjusts the liability to its present value by recognizing accretion expense as an operating expense in the consolidated statements of operations each period, and the capitalized cost is depreciated over the useful life of the related asset. Upon settlement of the liability, the Company records a gain or loss if the actual costs differ from the accrued amount. The Company has recorded asset retirement obligations (“AROs”) identified as part of the Business Combination in other long-term liabilities in order to recognize legal obligations associated with the retirement of tangible long-lived assets. The Company has assessed whether an ARO is required at each manufacturing facility and has recorded an obligation for those locations for which an obligation exists. The most significant of these are primarily attributable to environmental remediation liabilities associated with current operations that were incurred during the course of normal operations. The Company has AROs that are conditional in nature. The Company identified certain conditional AROs upon which it was able to reasonably estimate their fair value and recorded a liability. These AROs were triggered upon commitments by the Company to comply with local, state, and national laws to remove environmentally hazardous materials. The AROs have been recognized on a discounted basis using a credit adjusted risk free rate. Accretion of the AROs is recorded in other operating expense, net in the Company’s consolidated statements of operations. The following table includes the changes in the Company’s ARO liability during the years ended December 31, 2018 and 2017 : Years ended 2018 2017 Beginning balance $ 4,094 $ 3,700 Accretion expense 287 232 Foreign exchange impact (157 ) 162 Ending balance $ 4,224 $ 4,094 Environmental Expenditures. Environmental expenditures that pertain to current operations or to future revenues are expensed or capitalized consistent with the Company’s capitalization policy for property, plant and equipment. Expenditures that result from the remediation of an existing condition caused by past operations and that do not contribute to current or future revenues are expensed. Liabilities are recognized for remedial activities when the remediation is probable and the cost can be reasonably estimated. Recoveries of expenditures for environmental remediation are recognized as assets only when recovery is deemed probable. See Note 23 to these consolidated financial statements regarding commitments and contingencies and Note 15 regarding the accrued environmental reserve. Deferred Financing Costs. Financing costs incurred in connection with the issuance of long-term debt are deferred and presented as a direct reduction from the related debt instruments on the Company’s consolidated balance sheets. Deferred financing costs are amortized as interest expense using the effective interest method over the respective terms of the associated debt instruments. Stock-Based Compensation. The Company applies the fair value based method to account for stock options, restricted stock awards and restricted stock units issued in connection with its equity incentive plans. Stock-based compensation expense is recognized on a straight-line basis over the vesting periods of the respective awards, and the Company accounts for forfeitures of equity incentive awards as they occur. In connection with the vesting of restricted stock awards and restricted stock units, shares of common stock may be delivered to the Company by employees to satisfy withholding tax obligations at the instruction of the employee award holders. These transactions when they occur are accounted for as stock repurchases by the Company, with the shares returned to treasury stock at a cost representing the payment by the Company of the tax obligations on behalf of the employees in lieu of shares for the vesting event. See Note 22 to these consolidated financial statements regarding compensation expense associated with the Company’s equity incentive awards. Pensions and Postretirement Benefits. The Company maintains qualified and non-qualified defined benefit pension plans that cover employees in the United States and Canada, as well as certain employees in other international locations. Benefits for a majority of the plans are based on average final pay and years of service. Our funding policy, consistent with statutory requirements, is based on actuarial computations utilizing the projected unit credit method of calculation. Not all defined benefit pension plans are funded. In the United States and Canada, the pension plans’ assets include equity and fixed income securities. In our other international locations, the pension plans’ assets include equity and fixed income securities, as well as insurance contracts. Certain assumptions are made regarding the occurrence of future events affecting pension costs, such as mortality, withdrawal, disablement and retirement, changes in compensation and benefits, and discount rates to reflect the time value of money. The major elements in determining pension income and expense are pension liability discount rates and the expected return on plan assets. The Company references rates of return on high-quality, fixed income investments when estimating the discount rate, and the expected period over which payments will be made based upon historical experience. The long-term rate of return used to calculate the expected return on plan assets is the average rate of return estimated to be earned on invested funds for providing pension benefits. In addition to pension benefits, the Company provides certain health care benefits for employees who meet age, participation and length of service requirements at retirement. The Company uses explicit assumptions using the best estimates available of the plan’s future experience. Principal actuarial assumptions include: discount rates, present value factors, retirement age, participation rates, mortality rates, cost trend rates, Medicare reimbursement rates and per capita claims cost by age. Current interest rates as of the measurement date are used for discount rates in present value calculations. The Company also has defined contribution plans covering domestic employees of the Company and certain subsidiaries. Contingencies. Certain conditions may exist as of the date the financial statements are issued, which may result in a loss to the Company but which will only be resolved when one or more future events occur or fail to occur. The Company’s management and its legal counsel assess such contingent liabilities, and such assessment inherently involves an exercise of judgment. In assessing loss contingencies related to legal proceedings that are pending against the Company or unasserted claims that may result in such proceedings, the Company and legal counsel evaluate the perceived merits of any legal proceedings or unasserted claims as well as the perceived merits of the amount of relief sought or expected to be sought therein. If the assessment of a contingency indicates that it is probable that a loss has been incurred a

New Accounting Standards

New Accounting Standards	12 Months Ended
	Dec. 31, 2018
Accounting Changes and Error Corrections [Abstract]
New Accounting Standards	3. New Accounting Standards: Recently Adopted Accounting Standards In August 2018, the Financial Accounting Standards Board (“FASB”) issued guidance which will align the requirements for capitalizing implementation costs incurred in a cloud computing arrangement (i.e., a hosting arrangement) that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. Capitalized implementation costs related to a hosting arrangement that is a service contract will be amortized over the term of the hosting arrangement, beginning when the module or component of the hosting arrangement is ready for its intended use. The guidance is effective for public companies for fiscal years beginning after December 15, 2019, including all interim periods within that fiscal year. Early adoption is permitted, and the guidance can be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company early adopted the guidance effective October 1, 2018 and has applied the guidance on a prospective basis for any implementation costs incurred subsequent to the adoption date, with no significant impact on the Company’s consolidated financial statements. In August 2017, the FASB issued amendments related to hedge accounting. The amendments expand hedge accounting for non-financial and financial risk components and revise the measurement methodologies to better align with an entity’s risk management activities. Separate presentation of hedge ineffectiveness is eliminated to provide greater transparency of the full impact of hedging by requiring presentation of the results of the hedged item and hedging instrument in a single financial statement line item. In addition, the amendments reduce complexity by simplifying the manner in which assessments of hedge effectiveness may be performed. The new guidance is effective for public companies for annual periods beginning after December 15, 2018, including interim periods within those years. Early adoption is permitted, and the guidance should be applied prospectively for the amended presentation and disclosure requirements, and through a cumulative-effect adjustment to beginning retained earnings for any cash flow and net investment hedges existing at the date of adoption. The Company early adopted the guidance effective January 1, 2018. The Company’s cash flow hedges in place at the date of adoption yielded an immaterial amount of ineffectiveness; therefore, the Company did not reflect an adjustment to beginning retained earnings upon adoption. The amended presentation and disclosure requirements are reflected under the new guidance in Note 18 to these consolidated financial statements. In May 2017, the FASB issued guidance to clarify which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. Under the new guidance, an entity should account for the effects of a change in a share-based payment award using modification accounting unless the fair value, vesting conditions and classification as either a liability or equity are all the same with respect to the award immediately prior to modification and the modified award itself. The new guidance is effective for annual periods beginning after December 15, 2017, including interim periods within those years, and the new guidance should be applied prospectively to awards modified on or after the adoption date. The Company adopted the new guidance on January 1, 2018 as required, with no impact on the Company’s consolidated financial statements upon adoption. In March 2017, the FASB issued guidance to improve the presentation of net periodic pension cost and net periodic postretirement benefit cost (collectively, “pension costs”). Under current GAAP, there are several components of pension costs which are presented net to arrive at pension costs as included in the income statement and disclosed in the notes. As part of this amendment to the existing guidance, the service cost component of pension costs will be bifurcated from the other components and included in the same line items of the income statement as compensation costs are reported. The remaining components will be reported together below operating income on the income statement, either as a separate line item or combined with another line item on the income statement and disclosed. Additionally, with respect to capitalization to inventory, fixed assets, etc., only the service cost component will be eligible for capitalization upon adoption of the guidance. The new guidance is effective for public companies for annual periods beginning after December 15, 2017, including interim periods within those years. The amendments should be applied retrospectively upon adoption with respect to the presentation of the service and other cost components of pension costs in the income statement, and prospectively for the capitalization of the service cost component in assets. The Company adopted the new guidance on January 1, 2018 as required. Prior to the adoption of the guidance, the Company reflected its pension costs within cost of goods sold and selling, general and administrative expenses in the consolidated statements of operations, depending on whether the costs were associated with employees involved in manufacturing or back office support functions. Under the new guidance, the service cost component of the Company’s pension costs remained in the same line items of the consolidated statements of operations, but the remaining components are now reported as part of nonoperating income in the other (income) expense, net line item of the consolidated statements of operations. Although the guidance requires retrospective application upon adoption, a practical expedient permits the Company to use the amounts disclosed in its pension and other post-retirement benefit plan note as its basis of estimation for the prior comparative periods. The Company utilized the practical expedient, and $1,616 and $2,651 of a net pension benefit for the years ended December 31, 2017 and 2016 , respectively, was reclassified to other expense (income), net. For the year ended December 31, 2018 , the amount of pension costs included in other expense (income), net was a net benefit of $3,625 . In January 2017, the FASB issued guidance that clarifies the definition of a business and provides revised criteria and a framework to determine whether an integrated set of assets and activities is a business. For public companies, the new guidance is effective for fiscal years beginning after December 15, 2017, including interim periods within those years. The Company adopted the new guidance on January 1, 2018 as required, with no impact on the Company’s consolidated financial statements upon adoption. In November 2016, the FASB issued guidance which clarifies the classification and presentation of changes in restricted cash on the statement of cash flows. The updates in the guidance require that the statement of cash flows explain the change during the period in the total of cash, cash equivalents and restricted cash when reconciling the beginning-of-period and end-of-period total amounts. The updates also require a reconciliation between cash, cash equivalents and restricted cash presented on the balance sheet to the total of the same amounts presented on the statement of cash flows. For public companies, the new guidance is effective for fiscal years beginning after December 15, 2017 and interim periods within those years, and the new guidance should be applied retrospectively to each period presented. The Company adopted the new guidance on January 1, 2018 as required. As of December 31, 2018 and 2017 , the Company had $1,872 and $1,048 , respectively, of restricted cash included in prepaid and other current assets on its consolidated balance sheets. Changes in the Company’s restricted cash balances prior to the adoption of the new guidance were reflected within cash flows from investing activities in the Company’s consolidated statements of cash flows. The prior comparative periods in the Company’s consolidated statements of cash flows have been updated to conform to the new guidance. See Note 28 to these consolidated financial statements for supplemental cash flow disclosures. In August 2016, the FASB issued guidance which clarifies the classification of certain cash receipts and cash payments in the statement of cash flows, including debt prepayment or extinguishment costs and distributions from equity method investees. For public companies, the new guidance is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, and the new guidance should be applied retrospectively to each period presented. The Company adopted the new guidance on January 1, 2018 as required. The Company applied the new guidance to the term loan refinancing that occurred during the year ended December 31, 2018 ; see Note 16 to these consolidated financial statements for further information on the debt refinancing transaction. The following is a summary of the impact of adopting the new statement of cash flows guidance on the Company’s consolidated statements of cash flows: Year ended December 31, 2017 Previously Reported Adjustments Revised Net cash provided by operating activities (1) $ 116,062 $ 49,111 $ 165,173 Net cash used in investing activities (2) (182,695 ) (13,287 ) (195,982 ) Net cash provided by (used in) financing activities (1) 68,944 (49,111 ) 19,833 Effect of exchange rate changes on cash, cash equivalents and restricted cash (6,858 ) — (6,858 ) Net change in cash, cash equivalents and restricted cash (2) (4,547 ) (13,287 ) (17,834 ) Cash, cash equivalents and restricted cash at beginning of period (2) 70,742 14,335 85,077 Cash, cash equivalents and restricted cash at end of period (2) $ 66,195 $ 1,048 $ 67,243 Year ended December 31, 2016 Previously Reported Adjustments Revised Net cash provided by operating activities (1) $ 119,720 $ 2,988 $ 122,708 Net cash provided by (used in) investing activities (2) (1,929,680 ) 13,917 (1,915,763 ) Net cash provided by (used in) financing activities (1) 1,861,433 (2,988 ) 1,858,445 Effect of exchange rate changes on cash, cash equivalents and restricted cash (5,886 ) — (5,886 ) Net change in cash, cash equivalents and restricted cash (2) 45,587 13,917 59,504 Cash, cash equivalents and restricted cash at beginning of period (2) 25,155 418 25,573 Cash, cash equivalents and restricted cash at end of period (2) $ 70,742 $ 14,335 $ 85,077 (1) Adjustments include the reclassification of $47,875 in debt prepayment penalties for the year ended December 31, 2017, which were paid in cash, that were associated with the Company’s repricing and refinancing activities. The adjustments also include the reclassification of $1,236 and $2,988 in third-party lender fees for the years ended December 31, 2017 and 2016, respectively, associated with the Company’s repricing and refinancing activities that were paid in cash. In accordance with the August 2016 guidance which clarifies the classification of certain cash receipts and cash payments in the statement of cash flows, the amounts were reclassified from net cash provided by operating activities to net cash provided by (used in) financing activities. (2) In accordance with the November 2016 guidance that clarified the classification and presentation of changes in restricted cash on the statement of cash flows, the Company reclassified the changes in restricted cash for the respective periods from cash from investing activities to the cash, cash equivalents and restricted cash line item. In May 2014, the FASB issued accounting guidance (with subsequent targeted amendments) to significantly enhance comparability of revenue recognition practices across entities, industries, jurisdictions and capital markets. The core principle of the guidance is that revenue recognized from a transaction or event that arises from a contract with a customer should reflect the consideration to which an entity expects to be entitled in exchange for goods or services provided. To achieve that core principle, the new guidance sets forth a five-step revenue recognition model that will need to be applied consistently to all contracts with customers, except those that are within the scope of other topics in the Accounting Standards Codification (“ASC”). Also required are enhanced disclosures to help users of financial statements better understand the nature, amount, timing and uncertainty of revenues and cash flows from contracts with customers. The enhanced disclosures include qualitative and quantitative information about contracts with customers, significant judgments made in applying the revenue guidance, and assets recognized related to the costs to obtain or fulfill a contract. For public companies, the new requirements are effective for annual reporting periods beginning after December 15, 2017, including interim periods within those years. The Company reviewed its key revenue streams and assessed the underlying customer contracts within the framework of the new guidance. The Company evaluated the key aspects of its revenue streams for impact under the new guidance and performed a detailed analysis of its customer agreements to quantify the changes under the guidance. The Company concluded that the guidance did not have a material impact on its existing revenue recognition practices upon adoption on January 1, 2018. The Company implemented the guidance under the modified retrospective transition method of adoption. Comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. The impact of adoption of the new revenue recognition guidance was immaterial for the year ended December 31, 2018 , and there was no transition adjustment required upon adoption. See Note 4 to these consolidated financial statements for additional disclosures required by the new guidance. Accounting Standards Not Yet Adopted as of December 31, 2018 In August 2018, the FASB issued guidance which modifies the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans. The guidance eliminates certain disclosure requirements, including the amounts in accumulated other comprehensive income expected to be recognized as components of net periodic benefit cost over the next fiscal year and the effects of a one-percentage point change in assumed health care cost trend rates. The guidance also requires additional disclosure of the reasons for significant gains and losses related to changes in the benefit obligation for the period. The guidance is effective for fiscal years ending after December 15, 2020 with early adoption permitted, and is required to be applied on a retrospective basis to all periods presented. The Company will modify its benefit plan disclosures in accordance with the new guidance upon adoption, and the guidance will not have a material impact on its consolidated financial statements. In August 2018, the FASB issued guidance which modifies certain disclosure requirements over fair value measurements. The guidance is effective for fiscal years beginning after December 15, 2019, including all interim periods within that fiscal year. The Company believes that the new guidance will not have a material impact on its consolidated financial statements. In June 2018, the FASB issued guidance which conforms the accounting for the issuance of all share-based payments using the same accounting model. Previously, the accounting for share-based payments to non-employees was covered under a different framework than those made to employees. Under the new guidance, awards to both employees and non-employees will essentially follow the same model, with small variations related to determining the term assumption when valuing a non-employee award as well as a different expense attribution model for non-employee awards. The new guidance is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. The Company is currently evaluating the effect that the new guidance would have on its consolidated financial statements. In February 2018, the FASB issued guidance which will permit entities to make an election to reclassify income tax effects stranded in accumulated other comprehensive income (“AOCI”) to retained earnings as a result of tax reform legislation enacted by the U.S. government on December 22, 2017. The standard is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, with early adoption permitted in any interim period for which the financial statements have not yet been issued. Prior to the enactment of the tax reform legislation on December 22, 2017, the Company had amounts recorded in AOCI related to its domestic pension, postretirement and supplementary benefit plans and cash flow hedging relationships that were based on pre-enactment tax rates. The Company is evaluating the impact that the new guidance will have on its consolidated financial statements. If the Company makes the election to reclassify the stranded income tax effects from AOCI, it may do so using one of two transition methods: retrospectively, or at the beginning of the period of adoption. In January 2017, the FASB issued guidance which eliminates the second step from the traditional two-step goodwill impairment test. Under current guidance, an entity performed the first step of the goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount; if an impairment loss was indicated, the entity computed the implied fair value of goodwill to determine whether an impairment loss existed, and if so, the amount to recognize. Under the new guidance, an impairment loss is recognized for the amount by which the carrying amount exceeds the reporting unit’s fair value (the Step 1 test), with no further testing required. Any impairment loss recognized is limited to the amount of goodwill allocated to the reporting unit. The new guidance is effective for public companies that are Securities and Exchange Commission (“SEC”) registrants for fiscal years beginning after December 15, 2019, with early adoption permitted for goodwill impairment tests performed on testing dates after January 1, 2017. The Company will apply the guidance prospectively to goodwill impairment tests subsequent to the adoption date. In June 2016, the FASB issued guidance that affects loans, trade receivables and any other financial assets that have the contractual right to receive cash. Under the new guidance, an entity is required to recognize expected credit losses rather than incurred losses for financial assets. The new guidance is effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years. The Company believes that the new guidance will not have a material impact on its consolidated financial statements. In February 2016, the FASB issued guidance (with subsequent targeted amendments) that modifies the accounting for leases. Under the new guidance, a lessee will recognize assets and liabilities for most leases (including those classified under existing GAAP as operating leases, which based on current standards are not reflected on the balance sheet), but will recognize expenses similar to current lease accounting. The new guidance also requires companies to provide expanded disclosures regarding leasing arrangements. For public companies, the new guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those years, with early adoption permitted. The new guidance must be adopted using a modified retrospective transition method. The Company can choose to apply the new guidance at the beginning of the earliest period presented in the financial statements, or at the date of adoption, with a cumulative-effect adjustment to the opening balance of retained earnings and no recast of prior period results presented within the Company’s consolidated financial statements. The Company has elected to apply the new guidance as of the date of adoption. The Company has operating lease agreements for which it expects to recognize right of use assets and corresponding liabilities on its balance sheet upon adoption of the new guidance. The Company is currently finalizing its lease portfolio analysis which will result in a material increase in total assets and liabilities in its consolidated balance sheets. The Company does not believe that the new guidance will have a material impact on its results of operations or cash flows. In addition, the Company has implemented a lease technology software to assist in its ongoing lease data collection and analysis. The Company is also updating its processes, accounting policies and internal controls to ensure it will meet the requirements of the new guidance upon adoption. The new guidance provides practical expedients, which the Company is currently finalizing its evaluation. The Company has elected the short term lease accounting policy and will not record right of use assets or lease liabilities for leases with a term of twelve months or less. The Company has elected the package of practical expedients which provides for an entity not to reassess: (1) whether any expired or existing contracts are, or contain, leases; (2) the lease clarification for any expired or existing leases; and (3) initial direct costs for any existing leases.

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Dec. 31, 2018
Revenue from Contracts with Customers [Abstract]
Revenue from Contracts with Customers	4. Revenue from Contracts with Customers: Revenue Recognition Model As described in Note 2 , the Company applies the five-step revenue recognition model to each contract with its customers. Evidence of a contract between the Company and its customers may take the form of a master service agreement (“MSA”), a MSA in combination with an underlying purchase order, a combination of a pricing quote with an underlying purchase order or an individual purchase order received from a customer. The Company and certain of its customers enter into MSAs that establish the terms, including prices, under which orders to purchase goods may be placed. In cases where the MSA contains a distinct order for goods or contains an enforceable minimum quantity to be purchased by the customer, the Company considers the MSA to be evidence of a contract between the Company and its customer as the MSA creates enforceable rights and obligations. In cases where the MSA does not contain a distinct order for goods, the Company’s contract with a customer is the purchase order issued under the MSA. Customers of the Company may also negotiate orders via pricing quotes, which typically detail product pricing, delivery terms and payment information. When a customer procures goods under this method, the Company considers the combination of the pricing quote and the purchase order to create enforceable rights and obligations. Absent either a MSA or pricing quote, the Company considers an individual purchase order remitted by a customer to create enforceable rights and obligations. The Company identifies a performance obligation in a contract for each promised good that is separately identifiable from other promises in the contract and for which the customer can benefit from the good. The majority of the Company’s contracts have a single performance obligation, which is the promise to transfer individual goods to the customer. Single performance obligations are satisfied according to the shipping terms noted within the MSA or purchase order. The Company has certain contracts that include multiple performance obligations under which the purchase price for each distinct performance obligation is defined in the contract. These distinct performance obligations may include stand-ready provisions, which are arrangements to provide a customer assurance that they will have access to output from the Company’s manufacturing facilities, or monthly reservations of capacity fees. The Company considers stand-ready provisions and reservation of capacity fees to be performance obligations satisfied over time. Revenues related to stand-ready provisions and reservation of capacity fees are recognized on a ratable basis throughout the contract term and billed to the customer on a monthly basis. As described above, the Company’s MSAs with its customers may outline prices for individual products or contract provisions. MSAs in the Company’s performance chemicals and refining services product groups may contain provisions whereby raw material costs are passed-through to the customer per the terms of their contract. The Company’s exposure to fluctuations in raw material prices is limited, as the majority of pass-through contract provisions reset based on fluctuations in the underlying raw material price. MSAs in the Company’s refining services product group also contain take-or-pay arrangements, whereby the customer would incur a penalty in the form of a volume shortfall fee. There have been no issues where in which customers failed to meet the contractual minimum. Revenue from product sales are recorded at the sales price, which includes estimates of variable consideration for which reserves are established and which result from discounts, returns or other allowances that are offered within contracts between the Company and its customers. The Company recognizes revenues when performance obligations under the terms of a contract with its customer are satisfied, which generally occurs at a point in time by transferring control of a product to the customer. The Company determines the point in time when a customer obtains control of a product and the Company satisfies the performance obligation by considering factors including when the Company has a right to payment for the product, the customer has legal title to the product, the Company has transferred possession of the product, the customer has assumed the risks and rewards of ownership of the product and the customer has accepted the product. Revenue is measured as the amount of consideration the Company expects to receive in exchange for transferring goods. The Company does not have any significant payment terms as payment is received at, or shortly after, the point of sale. Environmental Catalysts & Services Segment - Silica Catalysts The Company’s silica catalysts product group sells highly customized products to its customers. Contracts between silica catalysts and its customers are typically evidenced by entering into a supply arrangement that outlines the specification of the products to be sold and contains terms and conditions under which purchase orders are issued. These supply arrangements typically have a duration from 1 to 10 years. Although the duration of these supply arrangements are in excess of one year, a contract is formed between the Company and its customer upon receipt of a purchase order. Certain silica catalysts supply arrangements contain performance guarantees whereby the goods sold under a purchase order can be returned if the goods are not compatible with the customer’s production process. In order to mitigate any risk of a customer returning goods, the Company will allow the customer to obtain a sample of the goods to ensure compliance with its production process before accepting any orders. Due to these mitigating factors, the Company has not experienced any returns and does not account for a separate performance obligation related to the performance guarantee in certain of its contracts. Environmental Catalysts & Services Segment - Refining Services Contracts between the Company’s refining services product group and its customers are typically evidenced by entering into a MSA which generally have a term in excess of one year. Though each MSA is unique, the terms may include performance obligations such as stand-ready provisions and minimum purchase requirements. Stand-ready provisions within these contracts are billed on a monthly basis, as the performance obligation resets on a monthly basis and does not carry-over to the following month. Certain of the Company’s refining services MSA’s contain minimum purchase requirements that expire within the calendar year. The Company reviews each contract with minimum purchase requirements to determine if the customer will meet the provisions within the current calendar year. The Company records revenues related to the minimum purchase requirements when it becomes evident that the customer will not meet the minimum purchase requirements noted within the contract. Contracts within refining services may also contain raw material pricing adjustments which are typically based on a commodity index. These raw material pass-through provisions reset on a periodic basis and prospectively adjust the raw material cost component of the goods sold to the customer. The Company accounts for the raw material costs on a prospective basis, as the price changes affect the future consideration of the sale of goods. Performance Materials & Chemicals - Performance Chemicals Contracts between the Company’s performance chemicals product group and its customers are typically evidenced by entering into a supply arrangement that outlines the specification of the products to be sold and contains terms and conditions under which purchase orders are issued. Certain performance chemicals supply arrangements may contain raw material pricing adjustments which are typically based on a commodity index. These raw material pass-through provisions reset on a periodic basis and prospectively adjust the raw material cost component of the goods sold to the customer. The Company accounts for the raw material pass-through costs on a prospective basis, as the price changes affect the future consideration of the sale of goods. Performance Materials & Chemicals - Performance Materials Contracts between the Company’s performance materials reporting unit and its customers are typically evidenced by receipt of a purchase order from the customer which details the specification of the products to be sold. Revenue is recorded according to the shipping terms noted within the purchase order. Contract Assets and Liabilities A contract asset is a right to consideration in exchange for goods that the Company has transferred to a customer when that right is conditional on something other than the passage of time. A contract liability exists when the Company receives consideration in advance of performance obligations. The Company has not recorded any contract assets or contract liabilities on its consolidated balance sheet as of December 31, 2018 . Practical Expedients and Accounting Policy Elections The Company has elected to use certain practical expedients and has made certain accounting policy elections as permitted under the new revenue recognition guidance. Certain of the Company’s contracts with customers are based on an individual purchase order; thus, the duration of these contracts are for one year or less. As described above, certain performance obligations reset either monthly or at the end of the calendar year. The Company has made an accounting policy election to omit certain disclosures related to remaining performance obligations for contracts which have an initial term of one year or less. The Company uses an output method to recognize revenues related to performance obligations satisfied over time. These performance obligations, as described above, are satisfied within a calendar year. As such, the Company has elected to utilize the “as-invoiced” practical expedient, which permits the Company to recognize revenue in the amount to which it has a right to invoice the customer, provided that the amount corresponds directly with the value provided by the performance obligation as completed to date. When the Company performs shipping and handling activities after the transfer of control to the customer (e.g. when control transfers prior to delivery), they are considered fulfillment activities as opposed to separate performance obligations, and the Company recognizes revenue upon the transfer of control to the customer. Accordingly, the costs associated with these shipping and handling activities are accrued when the related revenue is recognized under the Company’s policy election. The Company expenses incremental costs of obtaining a contract as incurred if the expected amortization period of the asset that the Company would have recognized is one year or less. Sales, value added and other taxes the Company collects concurrent with revenue producing activities are excluded from revenues. Disaggregated Revenue The Company’s primary means of disaggregating revenues is by product group, which can be found in Note 13 to these consolidated financial statements. The Company’s portfolio of products are integrated into a variety of end uses, which are described in the table below. Key End Uses Key Products Industrial & process chemicals • Silicate precursors for the tire industry • Glass beads, or microspheres, for metal finishing end uses Fuels & emission control • Refinery catalysts • Emission control catalysts • Catalyst recycling services • Silicate for catalyst manufacturing Packaging & engineered plastics • Catalysts for high-density polyethlene and chemicals syntheses • Antiblocks for film packaging • Solid and hollow microspheres for composite plastics • Sulfur derivatives for nylon production Highway safety & construction • Reflective markings for roadways and airports • Silica gels for surface coatings Consumer products • Silica gels for edible oil and beer clarification • Precipitated silicas, silicates and zeolites for the dentifrice and dishwasher and laundry detergent applications Natural resources • Silicates for drilling muds • Hollow glass beads, or microspheres, for oil well cements • Silicates and alum for water treatment mining • Bleaching aids for paper The following table disaggregates the Company’s sales, by segment and end use, for the year ended December 31, 2018 : Environmental Catalysts & Services Performance Materials & Chemicals Total Industrial & process chemicals $ 77,952 $ 279,678 $ 357,630 Fuels & emission control (1) 246,452 — 246,452 Packaging & engineered plastics 131,181 130,996 262,177 Highway safety & construction (1) — 320,134 320,134 Consumer products — 272,576 272,576 Natural resources 72,076 80,432 152,508 Total segment sales 527,661 1,083,816 1,611,477 Inter-segment sales eliminations (3,323 ) — (3,323 ) Total $ 524,338 $ 1,083,816 $ 1,608,154 (1) As described in Note 1 , the Company experiences seasonal sales fluctuations to customers in the fuels & emission control and highway safety & construction end uses.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	5. Fair Value Measurements: Fair values are based on quoted market prices when available. When market prices are not available, fair values are generally estimated using discounted cash flow analyses, incorporating current market inputs for similar financial instruments with comparable terms and credit quality. In instances where there is little or no market activity for the same or similar instruments, the Company estimates fair values using methods, models and assumptions that management believes a hypothetical market participant would use to determine a current transaction price. These valuation techniques involve some level of management estimation and judgment that becomes significant with increasingly complex instruments or pricing models. Where appropriate, adjustments are included to reflect the risk inherent in a particular methodology, model or input used. The Company’s financial assets and liabilities carried at fair value have been classified based upon a fair value hierarchy. The hierarchy gives the highest ranking to fair values determined using unadjusted quoted prices in active markets for identical assets and liabilities (Level 1) and the lowest ranking to fair values determined using methodologies and models with unobservable inputs (Level 3). The classification of an asset or a liability is based on the lowest level input that is significant to its measurement. For example, a Level 3 fair value measurement may include inputs that are both observable (Levels 1 and 2) and unobservable (Level 3). The levels of the fair value hierarchy are as follows: • Level 1—Values are unadjusted quoted prices for identical assets and liabilities in active markets accessible at the measurement date. Active markets provide pricing data for trades occurring at least weekly and include exchanges and dealer markets. • Level 2—Inputs include quoted prices for similar assets or liabilities in active markets, quoted prices from those willing to trade in markets that are not active, or other inputs that are observable or can be corroborated by market data for the term of the instrument. Such inputs include market interest rates and volatilities, spreads and yield curves. • Level 3—Certain inputs are unobservable (supported by little or no market activity) and significant to the fair value measurement. Unobservable inputs reflect the Company’s best estimate of what hypothetical market participants would use to determine a transaction price for the asset or liability at the reporting date. The following table presents information about the Company’s assets and liabilities that were measured at fair value on a recurring basis as of December 31, 2018 and 2017 , and indicates the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value. December 31, 2018 Quoted Prices in Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Derivative contracts $ 20,768 $ — $ 20,768 $ — Restoration plan assets 4,244 4,244 — — Total $ 25,012 $ 4,244 $ 20,768 $ — Liabilities: Derivative contracts $ 2,026 $ — $ 2,026 $ — December 31, Quoted Prices in Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Derivative contracts $ 1,043 $ — $ 1,043 $ — Restoration plan assets 5,576 5,576 — — Total $ 6,619 $ 5,576 $ 1,043 $ — Liabilities: Derivative contracts $ 448 $ — $ 448 $ — The following table presents information about the Company’s assets and liabilities that were measured at fair value on a non-recurring basis as of December 31, 2016 . The Company performed its annual impairment test on its indefinite-lived intangible assets on October 1, 2018 and 2017 , respectively, and determined that no impairment existed. Refer to Note 14 to these consolidated financial statements for a description of the valuation techniques the Company utilized to determine such fair value and for the results of the impairment testing procedures performed during the October 1, 2016 testing period. As of Quoted Prices in Significant Other Significant Total Assets: Indefinite-lived trade names (1) $ 153,922 $ — $ — $ 153,922 $ (6,873 ) (1) Indefinite-lived trade names with a carrying amount of $160,795 were written down to their implied fair value of $153,922 as part of the Company’s annual impairment assessment on October 1, 2016. This resulted in an impairment charge of $6,873 , which was recorded to other operating expense, net, on the consolidated statements of operations. Restoration plan assets The fair values of the Company’s restoration plan assets are determined through quoted prices in active markets. Restoration plan assets are assets held in a Rabbi trust to fund the obligations of the Company’s defined benefit supplementary retirement plans and include various stock and fixed income mutual funds. See Note 20 to these consolidated financial statements regarding defined benefit supplementary retirement plans. The Company’s restoration plan assets are included in other long-term assets on its consolidated balance sheets. Gains and losses related to these investments are included in other expense, net in the Company’s consolidated statements of operations. Unrealized gains and losses associated with the underlying stock and fixed income mutual funds were immaterial as of December 31, 2018 and December 31, 2017 , respectively. Derivative contracts Derivative assets and liabilities can be exchange-traded or traded over-the-counter (“OTC”). The Company generally values exchange-traded derivatives using models that calibrate to market transactions and eliminate timing differences between the closing price of the exchange-traded derivatives and their underlying instruments. OTC derivatives are valued using market transactions and other market evidence whenever possible, including market-based inputs to models, model calibration to market transactions, broker or dealer quotations or alternative pricing sources with reasonable levels of price transparency. When models are used, the selection of a particular model to value an OTC derivative depends on the contractual terms of, and specific risks inherent in, the instrument as well as the availability of pricing information in the market. The Company generally uses similar models to value similar instruments. Valuation models require a variety of inputs, including contractual terms, market prices and rates, forward curves, measures of volatility, and correlations of such inputs. For OTC derivatives that trade in liquid markets, such as forward contracts, swaps and options, model inputs can generally be corroborated by observable market data by correlation or other means, and model selection does not involve significant management judgment. The Company has interest rate caps, natural gas swaps and cross currency swaps that are fair valued using Level 2 inputs. In addition, the Company applies a credit valuation adjustment to reflect credit risk which is calculated based on credit default swaps. To the extent that the Company’s net exposure under a specific master agreement is an asset, the Company utilizes the counterparty’s default swap rate. If the net exposure under a specific master agreement is a liability, the Company utilizes a default swap rate comparable to PQ Group Holdings. The credit valuation adjustment is added to the discounted fair value to reflect the exit price that a market participant would be willing to receive to assume the Company’s liabilities or that a market participant would be willing to pay for the Company’s assets.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	6. Accumulated Other Comprehensive Income (Loss): The following table presents the components of accumulated other comprehensive income (loss), net of tax, as of December 31, 2018 and 2017 : December 31, 2018 2017 Amortization and unrealized gains (losses) on pension and postretirement plans, net of tax of ($2,362) and ($4,761) $ (546 ) $ 7,412 Net changes in fair values of derivatives, net of tax of ($474) and ($584) 637 967 Foreign currency translation adjustments, net of tax of $5,154 and $790 (39,195 ) (4,068 ) Accumulated other comprehensive income (loss) $ (39,104 ) $ 4,311 The following table presents the tax effects of each component of other comprehensive income (loss) for the years ended December 31, 2018 , 2017 and 2016 : Years ended 2018 2017 2016 Pre-tax amount Tax benefit/ (expense) After-tax amount Pre-tax amount Tax benefit/ (expense) After-tax amount Pre-tax amount Tax benefit/ (expense) After-tax amount Defined benefit and other postretirement plans: Amortization and unrealized gains (losses) $ (10,357 ) $ 2,399 $ (7,958 ) $ (139 ) $ 38 $ (101 ) $ 11,664 $ (4,799 ) $ 6,865 Benefit plans, net (10,357 ) 2,399 (7,958 ) (139 ) 38 (101 ) 11,664 (4,799 ) 6,865 Net gain (loss) from hedging activities (441 ) 110 (331 ) (5,799 ) 2,209 (3,590 ) 7,350 (2,793 ) 4,557 Foreign currency translation (39,419 ) 4,364 (35,055 ) 66,438 (5,837 ) 60,601 (73,461 ) 6,627 (66,834 ) Other comprehensive income (loss) $ (50,217 ) $ 6,873 $ (43,344 ) $ 60,500 $ (3,590 ) $ 56,910 $ (54,447 ) $ (965 ) $ (55,412 ) The following table presents the change in accumulated other comprehensive income (loss), net of tax, by component for the years ended December 31, 2018 and 2017 : Defined benefit Net gain (loss) from hedging activities Foreign Total December 31, 2016 $ 7,513 $ 4,557 $ (65,781 ) $ (53,711 ) Other comprehensive income (loss) before reclassifications 6 (3,797) 61,713 57,922 Amounts reclassified from accumulated other comprehensive income (loss) (1) (107) 207 — 100 Net current period other comprehensive income (loss) (101) (3,590) 61,713 58,022 December 31, 2017 $ 7,412 $ 967 $ (4,068 ) $ 4,311 Other comprehensive loss before reclassifications (7,874) (257) (35,127) (43,258) Amounts reclassified from accumulated other comprehensive income (loss) (1) (84) (73) — (157) Net current period other comprehensive loss (7,958) (330) (35,127) (43,415) December 31, 2018 (546) 637 (39,195) (39,104) (1) See the following table for details about these reclassifications. Amounts in parentheses indicate credits to profit/loss. The following table presents the reclassifications out of accumulated other comprehensive income (loss) for the years ended December 31, 2018 and 2017 . Details about Accumulated Other Amount Reclassified from Accumulated Other Comprehensive Income (Loss) (a) Affected Line Item in the Years ended 2018 2017 Defined benefit and other postretirement plans: Amortization of prior service credit $ (112 ) $ (78 ) (b) Amortization of net (gain) loss 12 (54 ) (b) (100 ) (132 ) Total before tax 16 25 Tax expense (benefit) $ (84 ) $ (107 ) Net of tax Net (gain) loss from hedging activities: Interest rate caps $ 256 $ 40 Interest expense Natural gas swaps (353 ) 222 Cost of goods sold (97 ) 262 Total before tax 24 (55 ) Tax expense (benefit) $ (73 ) $ 207 Net of tax Total reclassifications for the period $ (157 ) $ 100 Net of tax (a) Amounts in parentheses indicate credits to profit/loss. (b) These accumulated other comprehensive income (loss) components are included in the computation of net periodic pension and other postretirement cost (see Note 20 to these consolidated financial statements for additional details).

Business Combination

Business Combination	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Business Combination	7. Business Combination: As described in Note 1 to these consolidated financial statements, on May 4, 2016, the Company, PQ Holdings, Eco Services, certain investment funds affiliated with CCMP and certain other stockholders of PQ Holdings and Eco Services completed the Business Combination. The Business Combination was accounted for using the acquisition method of accounting. Under the acquisition method, the purchase price is allocated to the net assets acquired based on the fair values of assets acquired and liabilities assumed as of the acquisition date. The excess of the purchase price over the fair values of these net assets is recorded as goodwill. The following table sets forth the calculation and allocation of the purchase price to the net assets acquired of PQ Holdings with respect to the Business Combination, which was complete as of December 31, 2016. Total consideration, net of cash acquired $ 2,689,941 Recognized amounts of identifiable assets acquired and liabilities assumed: Receivables $ 161,110 Inventories 254,770 Prepaid and other current assets 19,295 Investments in affiliated companies 472,994 Property, plant and equipment 683,673 Other intangible assets 754,000 Other long-term assets 48,127 Fair value of assets acquired 2,393,969 Revolver, notes payable & current debt (2,441 ) Accounts payable (93,222 ) Accrued liabilities (98,621 ) Long-term debt (20,470 ) Deferred income taxes (327,296 ) Other long-term liabilities (113,936 ) Noncontrolling interest (6,569 ) Fair value of net assets acquired 1,731,414 Goodwill 958,527 $ 2,689,941 Total consideration for the Business Combination included $1,777,740 of cash, $910,800 of equity in the acquired PQ Holdings entities and $1,400 of assumed stock awards of PQ Holdings. The fair value of the equity consideration was determined based on an estimated enterprise value using a market approach as of the date of the Business Combination, reduced by borrowings to arrive at the fair value of equity. The existing PQ Holdings credit facilities were not legally assumed as part of the Business Combination, and the extinguishment of the debt concurrent with the Business Combination was included as part of the consideration transferred (see Note 16 to these consolidated financial statements for further information). Acquisition costs of $1,583 are included in other operating expense, net in the Company’s consolidated statement of operations for the year ended December 31, 2016. The Company believes that its diverse range of industrial, consumer and governmental applications in which its products are used were the primary reasons that contributed to a total purchase price that resulted in the recognition of goodwill. The goodwill associated with the Business Combination is not deductible for tax purposes. The valuation of the intangible assets acquired and the related weighted-average amortization periods are as follows: Amount Weighted-Average Intangible assets subject to amortization: Trademarks $ 35,400 15.0 Technical know-how 189,300 20.0 Contracts 19,800 5.3 Customer relationships 268,700 10.6 In-process research and development 6,800 Total intangible assets subject to amortization 520,000 Trade names, not subject to amortization 151,100 Indefinite Trademarks, not subject to amortization 82,900 Indefinite Total $ 754,000 In accordance with the requirements of the purchase method of accounting for acquisitions, inventories were recorded at fair market value (which is defined as estimated selling prices less the sum of (a) costs of disposal and (b) a reasonable profit allowance for the selling effort of the acquiring entity), which was $58,683 higher than the historical cost. The Company’s cost of goods sold includes a pre-tax charge of $871 and $29,086 for the years ended December 31, 2017 and 2016, respectively, relating to the portion of the step-up on inventory sold during the period. A separate portion of the fair value step-up related to the domestic inventory accounted for under the LIFO method was included in inventory on the consolidated balance sheet as of December 31, 2016 as part of the new LIFO base layer on the acquired inventory (see Note 10 to these consolidated financial statements for further information). The Company’s consolidated financial statements include PQ Holdings results of operations from May 4, 2016 through December 31, 2016. Sales and net loss attributable to PQ Holdings during this period are included in the Company’s consolidated financial statements for the year ended December 31, 2016 and total $690,459 and $17,991 , respectively. Pro Forma Financial Information The unaudited pro forma information has been derived from the Company’s historical consolidated financial statements and has been prepared to give effect to the Business Combination, assuming that the Business Combination occurred on January 1, 2015. These pro forma adjustments primarily relate to depreciation expense on stepped up fixed assets, amortization of acquired intangibles, cost of goods sold expense related to the sale of stepped up inventory, interest expense related to additional debt that would be needed to fund the Business Combination, and the estimated impact of these adjustments on the Company’s tax provision. The unaudited pro forma consolidated results of operations are provided for illustrative purposes and are not indicative of the Company’s actual consolidated results of operations or consolidated financial position. The unaudited pro forma results of operations do not reflect any operating efficiencies or potential cost savings which may result from the acquisitions. Year ended Pro forma sales $ 1,403,041 Pro forma net loss (76,994 ) The pro forma net loss for the year ended December 31, 2016 excludes certain charges that were allocated to the pro forma results for the year ended December 31, 2015. These non-recurring charges include a debt prepayment penalty of $26,250 , one-time refinancing charges of $4,747 and transaction fee charges of $1,795 . 8. Acquisition: Acquisitions are accounted for using the acquisition method of accounting. Under the acquisition method, the purchase price is allocated to the identifiable net assets acquired based on the fair values of the identifiable assets acquired and liabilities assumed as of the acquisition date. The excess of the purchase price over the fair values of the identifiable net assets acquired is recorded to goodwill. On June 12, 2017 (the “Acquisition Date”), the Company acquired the facilities of Sovitec Mondial S.A. (“Sovitec”) located in Belgium, Spain, Argentina and France as part of a stock transaction (the “Acquisition”) for $41,572 in cash, excluding assumed debt. Based in Fleurus, Belgium, Sovitec is a high quality producer of engineered glass products used in transportation safety, metal finishing and polymer additives. The results of operations of Sovitec have been included in the Company’s consolidated financial statements since the Acquisition Date. The following table sets forth the calculation and allocation of the purchase price to the identifiable net assets acquired with respect to the Acquisition, which was complete as of March 31, 2018: Provisional Purchase Adjustments Purchase Total consideration, net of cash acquired $ 41,572 $ — $ 41,572 Recognized amounts of identifiable assets acquired and liabilities assumed: Receivables $ 14,305 $ — $ 14,305 Inventories 7,645 1,603 9,248 Prepaid and other current assets 400 — 400 Property, plant and equipment 9,020 15,960 24,980 Other intangible assets — 5,753 5,753 Other long-term assets 129 15,921 16,050 Fair value of assets acquired 31,499 39,237 70,736 Current debt (6,420 ) — (6,420 ) Accounts payable (10,748 ) — (10,748 ) Long-term debt (10,189 ) — (10,189 ) Deferred income taxes — (4,426 ) (4,426 ) Other long-term liabilities (154 ) — (154 ) Fair value of net assets acquired 3,988 34,811 38,799 Goodwill 37,584 (34,811 ) 2,773 $ 41,572 $ — $ 41,572 As of the Acquisition Date, the fair value of accounts receivable approximated historical cost. The gross contractual amount of accounts receivable at the Acquisition Date was $14,607 , of which $302 was deemed uncollectible. The fair value of inventory is defined as estimated selling prices less the sum of (a) costs of disposal and (b) a reasonable profit allowance for the selling effort of the acquiring entity, which was $1,603 higher than the historical cost. The Company’s cost of goods sold for the year ended December 31, 2018 includes a pre-tax charge of $1,603 relating to the step-up on inventory, $108 of additional amortization expense related to identified intangible assets and $421 of additional depreciation expense, which would have been recorded during the year ended December 31, 2017 if the adjustments to the provisional amounts had been recognized as of the Acquisition Date. The Company’s other expense, net for the year ended December 31, 2018 includes additional amortization expense related to identified intangible assets of $101 which would have been recorded during the year ended December 31, 2017 if the adjustments to the provisional amounts had been recognized as of the Acquisition Date. The Company’s provision for income taxes for the year ended December 31, 2018 includes an additional $990 tax benefit associated with the year ended December 31, 2017, to reflect impacts as if the adjustments to the provisional amounts had been recognized as of the Acquisition Date. This amount is primarily a result of opening balance sheet adjustments recorded during the year ended December 31, 2018 , which needed to be re-measured through the income statement because of income tax rate changes that occurred subsequent to the Acquisition Date. The Company believes that the Acquisition will enable it to offer a more comprehensive, cost-effective and high-quality portfolio of products and services to its customers worldwide when, combined with anticipated synergies within its existing business, contributed to a total purchase price that resulted in the recognition of goodwill. All of the goodwill was assigned to the Company’s PM&C reporting segment. The goodwill associated with the Acquisition is not deductible for tax purposes. The valuation of the intangible assets acquired and the related weighted-average amortization periods are as follows: Amount Weighted-Average Intangible assets subject to amortization: Trademarks $ 1,767 11 Technical know-how 1,892 11 Total intangible assets subject to amortization 3,659 Trade names, not subject to amortization 2,094 Indefinite Total $ 5,753 The Company’s consolidated financial statements include Sovitec’s results of operations from June 12, 2017 through December 31, 2017. Sales and net income attributable to Sovitec during this period are included in the Company’s consolidated financial statements for the year ended December 31, 2017 and total $26,257 and $1,370 , respectively. Acquisition costs were immaterial for the year ended December 31, 2018 and were $2,515 for the year ended December 31, 2017. Acquisition costs are included in other operating expense, net in the Company’s consolidated statements of operations. Pro Forma Financial Information The unaudited pro forma financial information for the years ended December 31, 2017 and 2016 has been derived from the Company’s historical consolidated financial statements and prepared to give effect to the Acquisition, assuming that the Acquisition occurred on January 1, 2016. The unaudited pro forma consolidated results of operations are provided for illustrative purposes only and are not indicative of the Company’s actual consolidated results of operations had the Acquisition been made as of January 1, 2016. The unaudited pro forma results of operations do not reflect any operating efficiencies or potential cost savings which may result from the Acquisition. Years ended 2017 2016 Pro forma sales $ 1,488,528 $ 1,105,479 Pro forma net income (loss) 58,774 (78,234 ) Pro forma net income (loss) attributable to PQ Group Holdings Inc. 57,814 (78,822 ) Pro forma basic income (loss) per share $ 0.52 $ (1.01 ) Pro forma diluted income (loss) per share $ 0.52 $ (1.01 ) The results of operations for the year ended December 31, 2018 include the operating results of the combined company for the full period and therefore, there is no pro forma presentation for such periods included in the table above. Certain non-recurring charges included in the Company’s results of operations for the year ended December 31, 2017 were allocated to the respective prior year periods for pro forma purposes. For the year ended December 31, 2017, non-recurring charges allocated to the prior year period include transaction fee charges of $2,515 which were excluded from the pro forma net income for the year ended December 31, 2017. Included in pro forma net income for the year ended December 31, 2017 is amortization expense of $367 and depreciation expense of $760 associated with the fair value step-up of identifiable intangible assets and property, plant and equipment, respectively. Included in pro forma net loss for the year ended December 31, 2016 is amortization expense of $364 and depreciation expense of $467 associated with the fair value step-up of identifiable intangible assets and property, plant and equipment, respectively.

Acquisition

Acquisition	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Acquisitions	7. Business Combination: As described in Note 1 to these consolidated financial statements, on May 4, 2016, the Company, PQ Holdings, Eco Services, certain investment funds affiliated with CCMP and certain other stockholders of PQ Holdings and Eco Services completed the Business Combination. The Business Combination was accounted for using the acquisition method of accounting. Under the acquisition method, the purchase price is allocated to the net assets acquired based on the fair values of assets acquired and liabilities assumed as of the acquisition date. The excess of the purchase price over the fair values of these net assets is recorded as goodwill. The following table sets forth the calculation and allocation of the purchase price to the net assets acquired of PQ Holdings with respect to the Business Combination, which was complete as of December 31, 2016. Total consideration, net of cash acquired $ 2,689,941 Recognized amounts of identifiable assets acquired and liabilities assumed: Receivables $ 161,110 Inventories 254,770 Prepaid and other current assets 19,295 Investments in affiliated companies 472,994 Property, plant and equipment 683,673 Other intangible assets 754,000 Other long-term assets 48,127 Fair value of assets acquired 2,393,969 Revolver, notes payable & current debt (2,441 ) Accounts payable (93,222 ) Accrued liabilities (98,621 ) Long-term debt (20,470 ) Deferred income taxes (327,296 ) Other long-term liabilities (113,936 ) Noncontrolling interest (6,569 ) Fair value of net assets acquired 1,731,414 Goodwill 958,527 $ 2,689,941 Total consideration for the Business Combination included $1,777,740 of cash, $910,800 of equity in the acquired PQ Holdings entities and $1,400 of assumed stock awards of PQ Holdings. The fair value of the equity consideration was determined based on an estimated enterprise value using a market approach as of the date of the Business Combination, reduced by borrowings to arrive at the fair value of equity. The existing PQ Holdings credit facilities were not legally assumed as part of the Business Combination, and the extinguishment of the debt concurrent with the Business Combination was included as part of the consideration transferred (see Note 16 to these consolidated financial statements for further information). Acquisition costs of $1,583 are included in other operating expense, net in the Company’s consolidated statement of operations for the year ended December 31, 2016. The Company believes that its diverse range of industrial, consumer and governmental applications in which its products are used were the primary reasons that contributed to a total purchase price that resulted in the recognition of goodwill. The goodwill associated with the Business Combination is not deductible for tax purposes. The valuation of the intangible assets acquired and the related weighted-average amortization periods are as follows: Amount Weighted-Average Intangible assets subject to amortization: Trademarks $ 35,400 15.0 Technical know-how 189,300 20.0 Contracts 19,800 5.3 Customer relationships 268,700 10.6 In-process research and development 6,800 Total intangible assets subject to amortization 520,000 Trade names, not subject to amortization 151,100 Indefinite Trademarks, not subject to amortization 82,900 Indefinite Total $ 754,000 In accordance with the requirements of the purchase method of accounting for acquisitions, inventories were recorded at fair market value (which is defined as estimated selling prices less the sum of (a) costs of disposal and (b) a reasonable profit allowance for the selling effort of the acquiring entity), which was $58,683 higher than the historical cost. The Company’s cost of goods sold includes a pre-tax charge of $871 and $29,086 for the years ended December 31, 2017 and 2016, respectively, relating to the portion of the step-up on inventory sold during the period. A separate portion of the fair value step-up related to the domestic inventory accounted for under the LIFO method was included in inventory on the consolidated balance sheet as of December 31, 2016 as part of the new LIFO base layer on the acquired inventory (see Note 10 to these consolidated financial statements for further information). The Company’s consolidated financial statements include PQ Holdings results of operations from May 4, 2016 through December 31, 2016. Sales and net loss attributable to PQ Holdings during this period are included in the Company’s consolidated financial statements for the year ended December 31, 2016 and total $690,459 and $17,991 , respectively. Pro Forma Financial Information The unaudited pro forma information has been derived from the Company’s historical consolidated financial statements and has been prepared to give effect to the Business Combination, assuming that the Business Combination occurred on January 1, 2015. These pro forma adjustments primarily relate to depreciation expense on stepped up fixed assets, amortization of acquired intangibles, cost of goods sold expense related to the sale of stepped up inventory, interest expense related to additional debt that would be needed to fund the Business Combination, and the estimated impact of these adjustments on the Company’s tax provision. The unaudited pro forma consolidated results of operations are provided for illustrative purposes and are not indicative of the Company’s actual consolidated results of operations or consolidated financial position. The unaudited pro forma results of operations do not reflect any operating efficiencies or potential cost savings which may result from the acquisitions. Year ended Pro forma sales $ 1,403,041 Pro forma net loss (76,994 ) The pro forma net loss for the year ended December 31, 2016 excludes certain charges that were allocated to the pro forma results for the year ended December 31, 2015. These non-recurring charges include a debt prepayment penalty of $26,250 , one-time refinancing charges of $4,747 and transaction fee charges of $1,795 . 8. Acquisition: Acquisitions are accounted for using the acquisition method of accounting. Under the acquisition method, the purchase price is allocated to the identifiable net assets acquired based on the fair values of the identifiable assets acquired and liabilities assumed as of the acquisition date. The excess of the purchase price over the fair values of the identifiable net assets acquired is recorded to goodwill. On June 12, 2017 (the “Acquisition Date”), the Company acquired the facilities of Sovitec Mondial S.A. (“Sovitec”) located in Belgium, Spain, Argentina and France as part of a stock transaction (the “Acquisition”) for $41,572 in cash, excluding assumed debt. Based in Fleurus, Belgium, Sovitec is a high quality producer of engineered glass products used in transportation safety, metal finishing and polymer additives. The results of operations of Sovitec have been included in the Company’s consolidated financial statements since the Acquisition Date. The following table sets forth the calculation and allocation of the purchase price to the identifiable net assets acquired with respect to the Acquisition, which was complete as of March 31, 2018: Provisional Purchase Adjustments Purchase Total consideration, net of cash acquired $ 41,572 $ — $ 41,572 Recognized amounts of identifiable assets acquired and liabilities assumed: Receivables $ 14,305 $ — $ 14,305 Inventories 7,645 1,603 9,248 Prepaid and other current assets 400 — 400 Property, plant and equipment 9,020 15,960 24,980 Other intangible assets — 5,753 5,753 Other long-term assets 129 15,921 16,050 Fair value of assets acquired 31,499 39,237 70,736 Current debt (6,420 ) — (6,420 ) Accounts payable (10,748 ) — (10,748 ) Long-term debt (10,189 ) — (10,189 ) Deferred income taxes — (4,426 ) (4,426 ) Other long-term liabilities (154 ) — (154 ) Fair value of net assets acquired 3,988 34,811 38,799 Goodwill 37,584 (34,811 ) 2,773 $ 41,572 $ — $ 41,572 As of the Acquisition Date, the fair value of accounts receivable approximated historical cost. The gross contractual amount of accounts receivable at the Acquisition Date was $14,607 , of which $302 was deemed uncollectible. The fair value of inventory is defined as estimated selling prices less the sum of (a) costs of disposal and (b) a reasonable profit allowance for the selling effort of the acquiring entity, which was $1,603 higher than the historical cost. The Company’s cost of goods sold for the year ended December 31, 2018 includes a pre-tax charge of $1,603 relating to the step-up on inventory, $108 of additional amortization expense related to identified intangible assets and $421 of additional depreciation expense, which would have been recorded during the year ended December 31, 2017 if the adjustments to the provisional amounts had been recognized as of the Acquisition Date. The Company’s other expense, net for the year ended December 31, 2018 includes additional amortization expense related to identified intangible assets of $101 which would have been recorded during the year ended December 31, 2017 if the adjustments to the provisional amounts had been recognized as of the Acquisition Date. The Company’s provision for income taxes for the year ended December 31, 2018 includes an additional $990 tax benefit associated with the year ended December 31, 2017, to reflect impacts as if the adjustments to the provisional amounts had been recognized as of the Acquisition Date. This amount is primarily a result of opening balance sheet adjustments recorded during the year ended December 31, 2018 , which needed to be re-measured through the income statement because of income tax rate changes that occurred subsequent to the Acquisition Date. The Company believes that the Acquisition will enable it to offer a more comprehensive, cost-effective and high-quality portfolio of products and services to its customers worldwide when, combined with anticipated synergies within its existing business, contributed to a total purchase price that resulted in the recognition of goodwill. All of the goodwill was assigned to the Company’s PM&C reporting segment. The goodwill associated with the Acquisition is not deductible for tax purposes. The valuation of the intangible assets acquired and the related weighted-average amortization periods are as follows: Amount Weighted-Average Intangible assets subject to amortization: Trademarks $ 1,767 11 Technical know-how 1,892 11 Total intangible assets subject to amortization 3,659 Trade names, not subject to amortization 2,094 Indefinite Total $ 5,753 The Company’s consolidated financial statements include Sovitec’s results of operations from June 12, 2017 through December 31, 2017. Sales and net income attributable to Sovitec during this period are included in the Company’s consolidated financial statements for the year ended December 31, 2017 and total $26,257 and $1,370 , respectively. Acquisition costs were immaterial for the year ended December 31, 2018 and were $2,515 for the year ended December 31, 2017. Acquisition costs are included in other operating expense, net in the Company’s consolidated statements of operations. Pro Forma Financial Information The unaudited pro forma financial information for the years ended December 31, 2017 and 2016 has been derived from the Company’s historical consolidated financial statements and prepared to give effect to the Acquisition, assuming that the Acquisition occurred on January 1, 2016. The unaudited pro forma consolidated results of operations are provided for illustrative purposes only and are not indicative of the Company’s actual consolidated results of operations had the Acquisition been made as of January 1, 2016. The unaudited pro forma results of operations do not reflect any operating efficiencies or potential cost savings which may result from the Acquisition. Years ended 2017 2016 Pro forma sales $ 1,488,528 $ 1,105,479 Pro forma net income (loss) 58,774 (78,234 ) Pro forma net income (loss) attributable to PQ Group Holdings Inc. 57,814 (78,822 ) Pro forma basic income (loss) per share $ 0.52 $ (1.01 ) Pro forma diluted income (loss) per share $ 0.52 $ (1.01 ) The results of operations for the year ended December 31, 2018 include the operating results of the combined company for the full period and therefore, there is no pro forma presentation for such periods included in the table above. Certain non-recurring charges included in the Company’s results of operations for the year ended December 31, 2017 were allocated to the respective prior year periods for pro forma purposes. For the year ended December 31, 2017, non-recurring charges allocated to the prior year period include transaction fee charges of $2,515 which were excluded from the pro forma net income for the year ended December 31, 2017. Included in pro forma net income for the year ended December 31, 2017 is amortization expense of $367 and depreciation expense of $760 associated with the fair value step-up of identifiable intangible assets and property, plant and equipment, respectively. Included in pro forma net loss for the year ended December 31, 2016 is amortization expense of $364 and depreciation expense of $467 associated with the fair value step-up of identifiable intangible assets and property, plant and equipment, respectively.

Other Operating Expense, Net

Other Operating Expense, Net	12 Months Ended
	Dec. 31, 2018
Other Income and Expenses [Abstract]
Other Operating Expense, Net	9. Other Operating Expense, Net: A summary of other operating expense, net is as follows: Years ended 2018 2017 2016 Amortization expense $ 35,025 $ 32,010 $ 25,263 Transaction and other related costs (1) 776 7,415 4,952 Restructuring and other related costs (Note 24) 6,208 8,490 12,630 Net loss on asset disposals 6,574 5,793 4,216 Intangible asset impairment charge (Note 14) — — 6,873 Management advisory fees (Note 26) — 3,777 3,584 Insurance recoveries (2) (5,480 ) — — Write-off of long-term supply contract obligation (Note 25) (20,612 ) — — Other, net 6,959 6,740 4,783 $ 29,450 $ 64,225 $ 62,301 (1) Transaction and other related costs for the years ended December 31, 2018 and 2017 primarily include transaction costs associated with the Company’s IPO, exclusive of the direct costs recorded in stockholders’ equity net of the proceeds from the offering (see Note 1 to these consolidated financial statements for further information) and the Acquisition (see Note 8 ). Transaction and other related costs for the year ended December 31, 2016 primarily include transaction costs directly attributable to the Business Combination (see Note 7 ) as well as other business development costs. (2) During the year ended December 31, 2018 , the Company recognized $6,450 of insurance recoveries in its consolidated statement of operations related to the Company’s claim for losses sustained during Hurricane Harvey in August 2017. For the year ended December 31, 2018 , $5,480 was recorded as a gain in other operating expense, net, as reimbursement of expenses, $207 was recorded as a gain in net loss on asset disposals within other operating expense, net, for the Company’s previously recognized property losses, and $813 represented recoveries in excess of the Company’s property losses which was recorded as a non-operating gain in other expense, net, in the Company’s consolidated statement of operations.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventories	10. Inventories: Inventories are classified and valued as follows: December 31, 2018 2017 Finished products and work in process $ 206,188 $ 199,919 Raw materials 58,560 62,469 $ 264,748 $ 262,388 Valued at lower of cost or market: LIFO basis $ 160,863 $ 162,315 Valued at lower of cost and net realizable value: FIFO or average cost basis 103,885 100,073 $ 264,748 $ 262,388 The domestic inventory acquired as part of the Business Combination is valued based on the LIFO method. Therefore, the fair value allocated to the acquired LIFO inventory was treated as the new base inventory value. If inventories valued under the LIFO basis had been valued using the FIFO method, inventories would have been $18,263 and $26,630 lower than reported as of December 31, 2018 and 2017 , respectively, driven primarily by the purchase accounting fair value step-up of the LIFO inventory base value associated with the Business Combination. As of December 31, 2016, inventory quantities for one of the Company’s LIFO pools were reduced below their levels at the Business Combination date. As a result of this reduction, LIFO inventory costs charged to cost of goods sold were computed based on the lower base layer costs at the Business Combination date. The impact on cost of goods sold and net loss for the year ended December 31, 2016 was not material.

Investments in Affiliated Compa

Investments in Affiliated Companies	12 Months Ended
	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Investments in Affiliated Companies	11. Investments in Affiliated Companies: As a result of the Business Combination, the Company acquired investments in affiliated companies accounted for under the equity method. Affiliated companies accounted for on the equity method as of December 31, 2018 are as follows: Company Country Percent PQ Silicates Ltd. Taiwan 50% Zeolyst International USA 50% Zeolyst C.V. Netherlands 50% Quaker Holdings South Africa 49% Asociacion para el Estudio de las Tecnologias de Equipamiento de Carreteras, S.A. (“Aetec”) Spain 20% Following is summarized information of the combined investments (1) : December 31, 2018 2017 Current assets $ 215,416 $ 213,815 Noncurrent assets 248,288 235,440 Current liabilities 40,536 37,018 Noncurrent liabilities 56 1,417 Years ended December 31, 2018 2017 2016 Sales $ 352,599 $ 317,197 $ 206,072 Gross profit 126,945 132,812 91,761 Operating income 88,508 91,224 67,098 Net income 88,622 94,740 67,332 (1) Summarized information of the combined investments is presented at 100%; the Company’s share of the net assets and net income of affiliates is calculated based on the percent ownership specified in the table above. The Company’s investments in affiliated companies balance as of December 31, 2018 and 2017 includes net purchase accounting fair value adjustments of $258,066 and $264,700 , respectively, related to the Business Combination, consisting primarily of goodwill and intangible assets such as customer relationships, technical know-how and trade names. Consolidated equity in net income (loss) from affiliates is net of $6,634 , $8,599 and $36,296 of amortization expense related to purchase accounting fair value adjustments for the years ended December 31, 2018 , 2017 and 2016 , respectively. The following table summarizes the activity related to the Company’s investments in affiliated companies balance on the consolidated balance sheets: Years ended 2018 2017 Balance at beginning of period $ 469,276 $ 459,406 Acquisition — 119 Investments in affiliated companies 5,000 9,000 Equity in net income of affiliated companies 44,245 47,371 Charges related to purchase accounting fair value adjustments (6,634 ) (8,599 ) Dividends received (40,890 ) (44,071 ) Foreign currency translation adjustments (2,786 ) 6,050 Balance at end of period $ 468,211 $ 469,276 The Company had net receivables due from affiliates of $4,775 and $4,910 as of December 31, 2018 and 2017 , respectively, which are included in prepaid and other current assets. Net receivables due from affiliates are generally non-trade receivables. Sales to affiliates were $2,823 , $2,853 and $1,587 for the years ended December 31, 2018 , 2017 and 2016 , respectively. The Company purchased goods of $645 , $2,475 and $1,147 from affiliates, which is included in cost of goods sold during the years ended December 31, 2018 , 2017 and 2016 , respectively. On December 18, 2013, PQ Holdings and its joint venture, Zeolyst International, entered into a ten year real estate tax abatement agreement with the Unified Government of Wyandotte County, Kansas. The agreement utilizes an Industrial Revenue Bond financing structure to achieve a 75% real estate tax abatement on the value of the improvements that were constructed during the expansion of PQ Holdings and Zeolyst International’s facilities at the jointly-operated Kansas City, Kansas plant. A similar tax abatement agreement has been executed on an annual basis since December 18, 2013 with respect to additional plant expansions during those years. The financing obligations and the industrial bonds receivable have been presented net, as the financing obligations and the industrial bonds meet the criteria for right of setoff conditions under GAAP.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	12. Property, Plant and Equipment: A summary of property, plant and equipment, at cost, and related accumulated depreciation is as follows: December 31, 2018 2017 Land $ 190,772 $ 191,006 Buildings 212,284 200,054 Machinery and equipment 1,125,117 1,005,025 Construction in progress 102,185 145,414 1,630,358 1,541,499 Less: accumulated depreciation (421,379 ) (311,115 ) $ 1,208,979 $ 1,230,384 Depreciation expense was $132,640 , $124,551 and $89,453 for the years ended December 31, 2018 , 2017 and 2016 , respectively.

Reportable Segments

Reportable Segments	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Reportable Segments	13. Reportable Segments: The Company has organized its business around two operating segments based on the review of discrete financial results for each of the operating segments by the Company’s chief operating decision maker (the Company’s President and Chief Executive Officer), or CODM, for performance assessment and resource allocation purposes. Each of the Company’s operating segments represents a reportable segment under GAAP. The Company’s reportable segments are organized based on the nature and economic characteristics of the Company’s products. The Company’s two reportable segments are Environmental Catalysts and Services (“EC&S”) and Performance Materials and Chemicals (“PM&C”). The PM&C segment is a silicates and specialty materials producer with leading supply positions for the majority of its products sold in North America, Europe, South America, Australia and Asia (excluding China) serving end uses such as personal and industrial cleaning products, fuel efficient tires (or green tires), surface coatings, and food and beverage. The two product groups included in the PM&C segment are performance materials and performance chemicals. The EC&S segment is a leading global innovator and producer of catalysts for the refinery, emission control, and petrochemical industries and is also a leading provider of catalyst recycling services to the North American refining industry. The three product groups included in the EC&S segment are silica catalysts, zeolyst catalysts, and refining services. The EC&S segment includes equity in net income from Zeolyst International and Zeolyst C.V. (collectively, the “Zeolyst Joint Venture”), each of which are 50/50 joint ventures with CRI Zeolites Inc. (a wholly-owned subsidiary of Royal Dutch Shell). The Zeolyst Joint Venture is accounted for using the equity method in the Company’s consolidated financial statements (see Note 10 to these consolidated financial statements for further information). Company management evaluates the EC&S segment’s performance, including the Zeolyst Joint Venture, on a proportionate consolidation basis. Accordingly, the revenues and expenses used to compute the EC&S segment’s adjusted earnings before interest, income taxes, depreciation and amortization (“Adjusted EBITDA”) include the Zeolyst Joint Venture’s results of operations on a proportionate basis based on the Company’s 50% ownership level. Since the Company uses the equity method of accounting for the Zeolyst Joint Venture, these items are eliminated when reconciling to the Company’s consolidated results of operations. The Company’s management evaluates the operating results of each reportable segment based upon Adjusted EBITDA. Adjusted EBITDA consists of EBITDA, which is a measure defined as net income before depreciation and amortization, interest expense and income taxes (each of which is included in the Company’s consolidated statements of operations), and adjusted for certain items as discussed below. Summarized financial information for the Company’s reportable segments and product groups is shown in the following table: Years ended 2018 2017 2016 Sales: Silica Catalysts $ 72,099 $ 75,333 $ 53,029 Refining Services 455,562 398,342 373,718 Environmental Catalysts & Services (1) 527,661 473,675 426,747 Performance Chemicals $ 717,335 $ 687,645 $ 437,523 Performance Materials 378,279 324,225 206,522 Eliminations (11,798 ) (10,021 ) (5,094 ) Performance Materials & Chemicals 1,083,816 1,001,849 638,951 Inter-segment sales eliminations (2) (3,323 ) (3,423 ) (1,521 ) Total $ 1,608,154 $ 1,472,101 $ 1,064,177 Segment Adjusted EBITDA: (3) Environmental Catalysts & Services (4) $ 257,566 $ 243,587 $ 196,825 Performance Materials & Chemicals 243,357 240,128 158,679 Total Segment Adjusted EBITDA (5) $ 500,923 $ 483,715 $ 355,504 (1) Excludes the Company’s proportionate share of sales from the Zeolyst International and Zeolyst C.V. joint ventures (collectively, the “Zeolyst Joint Venture”) accounted for using the equity method (see Note 11 to these consolidated consolidated financial statements for further information). The proportionate share of sales is $156,687 , $143,774 and $94,516 for the years ended December 31, 2018 , 2017 and 2016 , respectively. (2) The Company eliminates intersegment sales when reconciling to the Company’s consolidated statements of operations. (3) The Company defines Adjusted EBITDA as EBITDA adjusted for certain items as noted in the reconciliation below. Management evaluates the performance of its segments and allocates resources based on several factors, of which the primary measure is Adjusted EBITDA. Adjusted EBITDA should not be considered as an alternative to net income as an indicator of the Company’s operating performance. Adjusted EBITDA as defined by the Company may not be comparable with EBITDA or Adjusted EBITDA as defined by other companies. (4) The Adjusted EBITDA from the Zeolyst Joint Venture included in the Environmental Catalysts and Services segment is $56,663 for the year ended December 31, 2018 , which includes $42,854 of equity in net income plus $6,634 of amortization of investment in affiliate step-up plus $12,592 of joint venture depreciation, amortization and interest. The Adjusted EBITDA from the Zeolyst Joint Venture included in the Environmental Catalysts and Services segment is $58,156 for the year ended December 31, 2017 , which includes $46,252 of equity in net income plus $8,600 of amortization of investment in affiliate step-up plus $11,070 of joint venture depreciation, amortization and interest. The Adjusted EBITDA from the Zeolyst Joint Venture included in the Environmental Catalysts and Services segment is $39,903 for the year ended December 31, 2016 , which includes $3,313 of equity in net loss plus $36,296 of amortization of investment in affiliate step-up plus $6,920 of joint venture depreciation, amortization and interest. (5) Total Segment Adjusted EBITDA differs from the Company’s consolidated Adjusted EBITDA due to unallocated corporate expenses. A reconciliation of net income (loss) attributable to PQ Group Holdings to Segment Adjusted EBITDA is as follows: Years ended 2018 2017 2016 Reconciliation of net income attributable to PQ Group Holdings Inc. to Segment Adjusted EBITDA Net income (loss) attributable to PQ Group Holdings Inc. $ 58,300 $ 57,603 $ (79,746 ) Provision for (benefit from) income taxes 28,995 (119,197 ) 10,041 Interest expense, net 113,723 179,044 140,315 Depreciation and amortization 185,234 177,140 128,288 Segment EBITDA 386,252 294,590 198,898 Unallocated corporate expenses 36,970 30,422 23,971 Joint venture depreciation, amortization and interest 12,592 11,070 6,920 Amortization of investment in affiliate step-up 6,634 8,600 36,296 Amortization of inventory step-up 1,603 871 29,086 Impairment of fixed assets, intangibles and goodwill — — 6,873 Debt extinguishment costs 7,751 61,886 13,782 Net loss on asset disposals 6,574 5,793 4,216 Foreign currency exchange loss (gain) 13,810 25,786 (3,558 ) LIFO expense 8,366 3,708 1,310 Management advisory fees — 3,777 3,583 Transaction and other related costs 893 7,425 4,664 Equity-based compensation 19,464 8,799 7,042 Restructuring, integration and business optimization expenses 14,019 13,174 16,258 Defined benefit pension plan cost (796 ) 2,940 1,375 Gain on contract termination (1) (20,612 ) — — Other 7,403 4,874 4,788 Segment Adjusted EBITDA $ 500,923 $ 483,715 $ 355,504 (1) Includes the non-cash write-off of a long-term supply contract obligation (see Note 25 ), which was recorded as a reduction in other operating expense, net in the consolidated statement of operations for the year ended December 31, 2018 . The Company’s consolidated results include equity in net income from affiliated companies of $37,611 and $38,772 for the years ended December 31, 2018 and 2017 , respectively, and equity in net loss from affiliated companies of $2,612 for the year ended December 31, 2016 . This is primarily comprised of equity in net income of $42,854 , $46,252 and $3,313 in the EC&S segment from the Zeolyst Joint Venture for the years ended December 31, 2018 , 2017 and 2016 , respectively. The remaining equity in net income (loss) for the Company is included in the PM&C segment, which is attributed to smaller investments and was not material. The Company’s equity in net income from affiliates was more than offset by $36,296 of amortization expense related to purchase accounting fair value adjustments associated with the Zeolyst Joint Venture for the year ended December 31, 2016 as a result of the Business Combination valuation. Capital expenditures for the Company’s reportable segments are shown in the following table: Years ended 2018 2017 2016 Capital expenditures: Environmental Catalysts & Services (1) $ 55,007 $ 53,145 $ 57,803 Performance Materials & Chemicals 75,476 84,783 71,293 Corporate (2) 1,205 2,554 (7,675 ) Capital expenditures per the consolidated statements of cash flows $ 131,688 $ 140,482 $ 121,421 (1) Excludes the Company’s proportionate share of capital expenditures from the Zeolyst Joint Venture. (2) Includes corporate capital expenditures, the cash impact from changes in capital expenditures in accounts payable and capitalized interest. Total assets by segment are not disclosed by the Company because the information is not prepared or used by the CODM to assess performance and to allocate resources. Sales and long-lived assets by geographic area are presented in the following tables. Sales are attributed to countries based upon location of products shipped. Years ended 2018 2017 2016 Sales (1) : United States $ 963,722 $ 874,764 $ 705,348 Netherlands 127,803 118,567 79,821 United Kingdom 119,586 116,410 67,494 Other foreign countries 397,043 362,360 211,514 Total $ 1,608,154 $ 1,472,101 $ 1,064,177 (1) Except for the United States, no sales in an individual country exceeded 10% of the Company’s total sales. December 31, 2018 2017 Long-lived assets (1) : United States $ 865,799 $ 891,861 Netherlands 52,461 52,882 United Kingdom 90,095 90,536 Other foreign countries 200,624 195,105 Total $ 1,208,979 $ 1,230,384 (1) Long-lived assets include property, plant and equipment, net.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	14. Goodwill and Other Intangible Assets: The changes in the carrying amount of goodwill for the years ended December 31, 2018 and 2017 is summarized as follows: Environmental Performance Total Balance as of December 31, 2016 $ 388,923 $ 852,506 $ 1,241,429 Goodwill recognized — 37,584 37,584 Foreign exchange impact 2,410 24,533 26,943 Balance as of December 31, 2017 $ 391,333 $ 914,623 $ 1,305,956 Goodwill recognized — 649 649 Goodwill adjustments (1) — (34,811 ) (34,811 ) Foreign exchange impact and other (1,682 ) (15,183 ) (16,865 ) Balance as of December 31, 2018 $ 389,651 $ 865,278 $ 1,254,929 (1) Represents the measurement period adjustments on the net assets acquired as part of the Acquisition (see Note 8 to these consolidated financial statements for further information regarding the Acquisition). The Company completed its annual goodwill impairment assessments as of October 1, 2018 and 2017 . For the annual assessments, the Company bypassed the option to perform the qualitative assessment and proceeded directly to performing the first step of the two-step goodwill impairment test for each of its reporting units. For each of the October 1, 2018 and 2017 assessments, the Company identified four reporting units, two in each of its operating segments (EC&S and PM&C). The Company determined the fair value of its reporting units using a split between a market approach and an income, or discounted cash flow, approach. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Estimating the fair value of a reporting unit requires various assumptions including the use of projections of future cash flows and discount rates that reflect the risks associated with achieving those cash flows. The key assumptions used in estimating the fair value were the operating margin growth rates, revenue growth rates from implementation of strategic plans, the weighted average cost of capital, the perpetual growth rate, and the estimated earnings market multiples of each reporting unit. The market value was estimated using publicly traded comparable company values by applying their most recent annual EBITDA multiples to the reporting unit’s trailing twelve months EBITDA. The income approach value was estimated using a discounted cash flow approach. The assumptions about future cash flows and growth rates are based on management’s assessment of a number of factors including the reporting unit’s recent performance against budget as well as management’s ability to execute on planned future strategic initiatives. Discount rate assumptions are based on an assessment of the risk inherent in those future cash flows. As of October 1, 2018 and 2017 , the fair values of each of the Company’s reporting units exceeded their respective carrying values and therefore, the second step of the two-step goodwill impairment test was not required. In addition to the annual goodwill impairment assessment, the Company also performed the annual impairment test over its other indefinite-lived intangible assets as of October 1, 2018 and 2017 . The fair values of these intangible assets were in excess of their carrying amounts as of the respective testing dates, and as such, there was no impairment of the Company’s indefinite-lived intangible assets for the years ended December 31, 2018 and 2017 . As a result of the Company’s 2016 test, the Company determined that the trade names related to its performance chemicals reporting unit within the PM&C segment and its catalysts reporting unit within the EC&S segment were impaired as of October 1, 2016. The impaired intangibles related to those identified as part of the Business Combination. The fair value of the respective trade names was determined using the relief-from-royalty method based on the discounted cash flows used in the goodwill impairment test. Slower sales growth rates for both reporting units led to the recognition of the impairment charges. Based on the testing performed, the Company recorded non-cash impairment charges of $5,350 related to trade names within the performance chemicals reporting unit and $1,523 related to trade names within the catalysts reporting unit for the year ended December 31, 2016 . The impairment charges are included in the other operating expense, net line item of the Company’s consolidated statement of operations. Gross carrying amounts and accumulated amortization for intangible assets other than goodwill are as follows: December 31, 2018 December 31, 2017 Gross Amount Accumulated Net Gross Amount Accumulated Net Balance Technical know-how $ 211,067 $ (32,112 ) $ 178,955 $ 212,599 $ (21,138 ) $ 191,461 Customer relationships 361,150 (95,399 ) 265,751 366,021 (63,860 ) 302,161 Contracts 19,800 (13,139 ) 6,661 19,800 (9,205 ) 10,595 Trademarks 36,657 (6,451 ) 30,206 35,202 (3,911 ) 31,291 Permits 9,100 (7,432 ) 1,668 9,100 (5,612 ) 3,488 Total definite-lived intangible assets 637,774 (154,533 ) 483,241 642,722 (103,726 ) 538,996 Indefinite-lived trade names 157,813 — 157,813 158,059 — 158,059 Indefinite-lived trademarks 80,582 — 80,582 82,289 — 82,289 In-process research and development 6,800 — 6,800 6,800 — 6,800 Total intangible assets $ 882,969 $ (154,533 ) $ 728,436 $ 889,870 $ (103,726 ) $ 786,144 The Company amortizes technical know-how over periods that range from eleven to twenty years, customer relationships over periods that range from seven to fifteen years, trademarks over an eleven to fifteen year period, contracts over periods that range from two to sixteen years, and permits over five years. Amortization of intangibles included in cost of goods sold on the consolidated statements of operations was $17,569 , $20,579 and $13,573 for the years ended December 31, 2018 , 2017 and 2016 , respectively. Amortization of intangibles included in other operating expense, net on the consolidated statements of operations was $35,025 , $32,010 and $25,263 for the years ended December 31, 2018 , 2017 and 2016 , respectively. Estimated future aggregate amortization expense of intangible assets is as follows: Year Amount 2019 $ 50,652 2020 47,101 2021 46,159 2022 46,092 2023 42,175 Thereafter 251,062 Total estimated future aggregate amortization expense $ 483,241

Accrued Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued Liabilities	15. Accrued Liabilities: The following table summarizes the components of accrued liabilities as follows: December 31, 2018 2017 Compensation and bonus $ 52,296 $ 49,988 Interest 21,933 15,936 Property tax 3,018 1,622 Environmental reserves (see Note 23) 4,693 5,790 Supply contract obligation (see Note 25) — 1,638 Income taxes 2,123 1,166 Commissions and rebates 1,798 1,820 Pension, postretirement and supplemental retirement plans (see Note 20) 2,439 2,192 Other 11,709 13,765 $ 100,009 $ 93,917

Long-term Debt

Long-term Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Long-term Debt	16. Long-term Debt: The summary of long-term debt is as follows: December 31, 2018 2017 Term Loan Facility (U.S. dollar denominated) $ — $ 916,153 Term Loan Facility (Euro denominated) — 335,808 New Term Loan Facility 1,157,498 — 6.75% Senior Secured Notes due 2022 625,000 625,000 5.75% Senior Unsecured Notes due 2025 300,000 300,000 ABL Facility — 25,000 Other 65,925 68,318 Total debt 2,148,423 2,270,279 Original issue discount (18,584 ) (18,390 ) Deferred financing costs (15,882 ) (21,403 ) Total debt, net of original issue discount and deferred financing costs 2,113,957 2,230,486 Less: current portion (7,237 ) (45,166 ) Total long-term debt, excluding current portion $ 2,106,720 $ 2,185,320 Senior Secured Credit Facilities Concurrent with the Business Combination, the Company entered into senior secured credit facilities (collectively, the “Senior Secured Credit Facilities”) comprised of a $1,200,000 term loan facility, which consisted of a $900,000 U.S. dollar-denominated tranche and a $300,000 Euro-denominated (or €265,000 ) tranche (the “Term Loan Facility”), and a $200,000 asset-based revolving credit facility (the “ABL Facility”). The Term Loan Facility was issued at 99.0% of the principal amount. Borrowings under the Term Loan Facility bore interest at a rate equal to the LIBOR rate (or EURIBOR rate, as applicable) or the base rate elected by the Company at the time of the borrowing plus a margin of 4.75% or 3.75% , respectively. Further, the LIBOR rate and base rate elected under the facilities were subject to a floor of 1.00% and 2.00% , respectively. The Term Loan Facility required minimum scheduled quarterly principal payments equal to 0.25% of the original principal amount of the term loans made on the closing date of the Business Combination. The Term Loan Facility had a maturity date of November 4, 2022. The existing PQ Holdings credit facilities were not legally assumed as part of the Business Combination, and the extinguishment of the debt was included as part of the consideration transferred for the Business Combination (see Note 7 to these consolidated financial statements for further information). Concurrent with entering into the Senior Secured Credit Facilities, the Company recorded $4,747 of new creditor and third-party financing costs as debt extinguishment costs. In addition, previous unamortized deferred financing costs of $6,252 and original issue discount of $989 associated with the previously outstanding debt were written off as debt extinguishment costs. On November 14, 2016 (the “First Amendment Closing Date”), the Company entered into the First Amendment Agreement to the Term Loan Facility (the “First Amendment”) pursuant to which the Company, among other things: (a) refinanced the existing $900,000 U.S. dollar-denominated tranche by issuing a U.S. dollar-denominated replacement term loan in the amount of $927,750 and (b) refinanced the existing €265,000 (or $300,000 ) Euro-denominated tranche by issuing a Euro-denominated replacement term loan in the amount of €283,338 . Included in the U.S. dollar-denominated replacement term loan was an additional $30,000 principal amount of borrowings. Included in the Euro-denominated replacement term loan was an additional €19,000 principal amount of borrowings. The borrowings under the First Amendment bore interest at a rate equal to the LIBOR rate plus a margin of 4.25% for U.S. dollar-denominated LIBOR Rate loans, the EURIBOR rate plus a margin of 4.00% for Euro-denominated LIBOR Rate loans, or the base rate plus a margin of 3.25% for base rate loans elected by the Company at the time of borrowing. These new replacement term loans had substantially the same terms under the original Term Loan Facility subject to the amendments contained in the First Amendment. Concurrent with the First Amendment, the Company recorded $474 of new creditor and third-party financing costs as debt extinguishment costs. In addition, previous unamortized deferred financing costs of $564 and original issue discount of $756 associated with the previously outstanding debt were written off as debt extinguishment costs. On August 7, 2017, the Company entered into the Second Amendment Agreement to the Term Loan Facility (the “Second Amendment”) and re-priced the then existing $927,750 U.S. dollar-denominated tranche and the then existing €283,338 Euro-denominated tranche of its term loans to reduce the applicable interest rates. The terms of the facilities were substantially consistent following the re-pricing, except that borrowings under the term loans bore interest at a rate equal to the LIBOR rate plus a margin of 3.25% with respect to U.S. dollar-denominated LIBOR rate loans and the EURIBOR rate plus a margin of 3.25% with respect to Euro-denominated EURIBOR rate loans. In addition, the LIBOR rate elected under the facilities was subject to a floor of 0% and the EURIBOR rate elected under the facilities was subject to a floor of 0.75% . Concurrent with the Second Amendment, the Company recorded $199 of new creditor and third-party financing costs as debt extinguishment costs. In addition, previous unamortized deferred financing costs of $105 and original issue discount of $162 associated with the previously outstanding debt were written off as debt extinguishment costs. On February 8, 2018 (the “Third Amendment Closing Date”), PQ Corporation (the “Borrower”), an indirect, wholly owned subsidiary of the Company, refinanced its existing U.S. Dollar and Euro denominated senior secured term loan facilities with a new $1,267,000 senior secured term loan facility (the “New Term Loan Facility”) by entering into the Third Amendment Agreement to the Term Loan Facility (the “Third Amendment”), which amended and restated the Term Loan Credit Agreement dated as of May 4, 2016, among the Borrower, CPQ Midco I Corporation, Credit Suisse AG, Cayman Island Branch, as administrative agent and collateral agent, and the lenders and the other parties party thereto from time to time (as amended prior to the Third Amendment, the “Existing Credit Agreement” and as amended and restated by the Amendment, the “New Credit Agreement”). The New Term Loan Facility bears interest at a floating rate of LIBOR plus 2.50% per annum and matures in February 2025, effectively lowering the interest rate margins compared to the refinanced term loan facilities, eliminating the interest rate floor that existed on the Euro-denominated tranche prior to refinancing, and extending the maturity of its senior secured term loan facility. The New Term Loan Facility requires scheduled quarterly amortization payments, each equal to 0.25% of the original principal amount of the loans under the New Term Loan Facility. Concurrent with the Third Amendment, the Company recorded $2,124 of new creditor and third-party financing costs as debt extinguishment costs. In addition, previous unamortized deferred financing costs of $1,403 and original issue discount of $2,352 associated with the previously outstanding debt were written off as debt extinguishment costs. On the Third Amendment Closing Date, the Company also entered into multiple cross currency swap arrangements to hedge foreign currency risk. The swaps are designed to enable the Company to effectively convert a portion of its fixed-rate U.S. dollar denominated debt obligations into approximately €280,000 equivalent ( $320,404 as of December 31, 2018 ). The swaps are expected to mature in February 2023. The Company may at any time or from time to time voluntarily prepay loans under the New Term Loan Facility in whole or in part without premium or penalty. The New Term Loan Facility requires mandatory prepayments from (i) 50% of “Excess Cash Flow” (as defined in the New Credit Agreement) on an annual basis with step downs to lower percentages based on the Borrower’s leverage ratio, if applicable, (ii) net cash proceeds from the issuance or incurrence of certain indebtedness and (iii) net cash proceeds received from certain non-ordinary course disposition of assets and casualty events to the extent such net cash proceeds were not reinvested in the Company’s business within a certain specified time period. Prepayments are applied to remaining amortization installments in direct order of maturity. The remaining principal balance of the term loans are due upon maturity. In addition, the New Credit Agreement contains customary affirmative and negative covenants and events of default, all of which are substantially the same as under the Existing Credit Agreement. The Borrower and certain Canadian and European subsidiaries of the Borrower also have a $200,000 asset-based revolving credit facility (the “ABL Facility”) which provides for $150,000 in U.S. available borrowings, up to $10,000 in Canadian available borrowings and up to $40,000 of European available borrowings. Borrowings under the ABL Facility bear interest at a rate equal to the LIBOR rate or the base rate elected by the Company at the time of the borrowing plus a margin of between 1.50% - 2.00% or 0.50% - 1.00% , respectively, depending on availability under the ABL Facility. In addition, there is an annual commitment fee equal to 0.375% , with a step-down to 0.25% based on the average usage of the revolving credit borrowings available. As of December 31, 2018 , there were no revolving credit borrowings under the ABL Facility. Revolving credit borrowings are payable at the option of the Company throughout the term of the ABL Facility with the balance due May 4, 2021. The Company has the ability to request letters of credit under the ABL Facility. The Company had $19,796 of letters of credit outstanding as of December 31, 2018 , which reduce available borrowings under the ABL Facility by such amounts. The New Term Loan Facility is guaranteed by CPQ Midco I Corporation, a subsidiary of the Company and the direct parent of the Borrower (“Holdings”) and substantially all of the Borrower’s wholly owned U.S. subsidiaries. The obligations under the New Term Facility are secured (i) by a first-priority security interest in, among other things, a pledge substantially all of the Borrower’s and the guarantors’ assets (other than collateral securing the ABL Facility on a first-priority basis) and (ii) by a second-priority security interest in receivables, inventory, deposit accounts and other collateral of the Borrower and the U.S. subsidiary guarantors securing the ABL Facility. The liens securing the Term Loan Facility and the guarantees are pari passu with the liens securing the Senior Secured Notes subject to the pari passu intercreditor agreement. The obligations of the Borrower under the ABL Facility are guaranteed by Holdings and the same U.S. subsidiary guarantors that guarantee the New Term Loan Facility, the obligations of the Canadian Borrowers under the ABL Facility are guaranteed by certain other Canadian subsidiaries of the Borrower and the obligations of the European Borrowers under the ABL Facility are guaranteed by certain other European subsidiaries of the Borrower. The obligations of the borrowers and guarantors under the ABL Facility are secured (i) by a first-priority security interest in, among other things, substantially all of their receivables, inventory, deposit accounts and other collateral securing the ABL Facility on a first-priority basis and (ii) by a second-priority security interest in the property and assets of Holdings, the Borrower and the U.S. subsidiary guarantors that secure the Term Loan Facility. In addition, the ABL Facility is secured by the equity interests in, and substantially all of the assets of, certain foreign guarantors in connection with the Canadian dollar-denominated and Euro-denominated availability. The Term Loan Facility and the ABL Facility contain various non-financial restrictive covenants. Each limits the ability of PQ Corporation and its restricted subsidiaries to incur certain indebtedness or liens, merge, consolidate or liquidate, dispose of certain property, make investments or declare or pay dividends, make optional payments, modify certain debt instruments, enter into certain transactions with affiliates, enter into certain sales and leasebacks, and certain other non-financial restrictive covenants. The ABL Facility also contains one financial covenant which applies when minimum availability under the ABL Facility exceeds a certain threshold. During such time, the Company is required to maintain a fixed-charge coverage ratio of at least 1 .0 to 1.0. The Company is in compliance with all debt covenants as of December 31, 2018 and 2017 , respectively. In September 2018, the Company prepaid $45,000 of outstanding principal balance on the New Term Loan Facility. The Company wrote off $258 of previously unamortized deferred financing costs and original issue discount of $606 as debt extinguishment costs. In December 2018, the Company prepaid $55,000 of outstanding principal balance on the New Term Loan Facility. The Company wrote off $301 of previously unamortized deferred financing costs and original issue discount of $707 as debt extinguishment costs. The prepayments were applied against the remaining scheduled installments of principal due in respect of the loans under the New Term Loan Facility in direct order of maturity. 6.75% Senior Secured Notes due 2022 Concurrent with the Business Combination, the Borrower issued $625,000 of 6.750% Senior Secured Notes due November 2022 (the “6.75% Senior Secured Notes”) in transactions exempt from or not subject to registration under the Securities Act pursuant to Rule 144A and Regulation S under the Securities Act of 1933. The 6.75% Senior Secured Notes are guaranteed by guaranteed by PQ Holdings Inc. and by the U.S. subsidiary guarantors that guarantee the New Term Loan Facility and are secured by liens on the assets of the Borrower and the U.S. subsidiary guarantors on a pari passu with the liens securing the New Term Loan Facility subject to the pari passu intercreditor agreement. The guarantee by PQ Holdings Inc. is unsecured. The indenture relating to the 6.75% Senior Secured Notes contains various limitations on the Company’s and its restricted subsidiaries’ ability to incur additional indebtedness, pay dividends or repay certain debt, make loans and investments, sell assets, create liens, enter into transactions with affiliates, enter into agreements restricting the Borrower’s subsidiaries ability to pay dividends, and merge and consolidate with other companies, among other things. Interest on the 6.75% Senior Secured Notes is payable on May 15 and November 15 of each year, commencing November 15, 2016. No principal payments are required with respect to the 6.75% Senior Secured Notes prior to their final maturity. The 6.75% Senior Secured Notes mature on November 15, 2022. If any Event of Default (other than a default relating to certain events of bankruptcy or insolvency of PQ Corporation or certain of its subsidiaries) occurs and is continuing under the Indenture, the Trustee or the Holders of at least 30% in principal amount of the then total outstanding notes by notice to the Company may declare the principal, premium, if any, interest and any other monetary obligations on all the then outstanding notes to be due and payable immediately. If an event of default arising from certain events of bankruptcy or insolvency of the Company occurs, the principal of, premium, if any, and interest on all the 6.75% Senior Secured Notes shall become immediately due and payable without any declaration or other act on the part of the trustee or any holders. The 6.75% Senior Secured Notes are redeemable, in whole or in part, at the redemption prices (expressed as percentages of principal amount of the 6.75% Senior Secured Notes to be redeemed) set forth below, plus accrued and unpaid interest, if any, to, but not including, the redemption date, if redeemed on or after any of the dates below until the subsequent date below: Year Percentage May 15, 2019 103.375% May 15, 2020 101.688% May 15, 2021 and thereafter 100.000% Upon the occurrence of a change of control, as defined, each holder will have the right to require the Company to purchase all or any part of such holder’s 6.75% Senior Secured Notes at a purchase price in cash equal to 101% of the principal amount, plus accrued and unpaid interest. Senior Unsecured Notes - Redeemed in 2017 Concurrent with the Business Combination, the Borrower issued $525,000 aggregate principal amount of floating rate Senior Unsecured Notes due 2022 (the “Senior Unsecured Notes”) in a concurrent private placement exempt from the registration requirements of the Securities Act. The notes were issued at 98.0% of the principal amount. The Senior Unsecured Notes were to mature on May 1, 2022. In conjunction with the Company’s IPO, on October 3, 2017, the Borrower redeemed $446,208 in aggregate principal of the $525,000 of its Senior Unsecured Notes using the proceeds from the IPO. Following the redemption, $78,792 aggregate principal amount of the Senior Unsecured Notes remained outstanding. The Borrower paid a redemption premium of $32,284 , which was recorded as debt extinguishment costs. In addition, previous unamortized deferred financing costs of $696 and original issue discount of $7,555 associated with the previously outstanding debt were written off as debt extinguishment costs. On December 11, 2017, the Borrower redeemed the remaining $78,792 aggregate principal amount of the Senior Unsecured Notes with the proceeds from its issuance of the 5.75% Senior Unsecured Notes due 2025. The Borrower paid a redemption premium of $7,091 , of which $6,043 was recorded as debt extinguishment costs. In addition, unamortized deferred financing costs of $108 and original issue discount of $1,176 associated with the previously outstanding debt were written off as debt extinguishment costs. Refer to the 5.75% Senior Unsecured Notes due 2025 section of this note for further information. 8.50% Senior Notes due 2022 - Redeemed in 2017 In December 2014, Eco Services issued $200,000 aggregate principal amount of 8.50% senior notes due 2022 (the “2022 Notes”) under an indenture dated October 24, 2014. The 2022 Notes were issued in a private transaction exempt from the registration requirements of the Securities Act. Pursuant to the indenture governing the 2022 Notes, PQ Group Holdings assumed the obligations of Eco Services under the 2022 Notes following the Business Combination. The 2022 Notes were to mature on November 1, 2022 and were issued at 100% of the principal amount. On December 11, 2017, the Borrower redeemed the $200,000 aggregate principal amount of the 2022 Notes with the proceeds from its issuance of the 5.75% Senior Unsecured Notes due 2025. The Borrower paid a redemption premium of $8,500 , of which $7,996 was recorded as debt extinguishment costs. In addition, unamortized deferred financing costs of $5,207 associated with the previously outstanding debt were written off as debt extinguishment costs. Refer to the 5.75% Senior Unsecured Notes due 2025 section of this note for further information. 5.75% Senior Unsecured Notes due 2025 On December 11, 2017, the Borrower issued $300,000 aggregate principal amount of floating rate Senior Unsecured Notes due 2025 (the “ 5.75% Senior Unsecured Notes”) in a private placement exempt from the registration requirements of the Securities Act. The 5.75% Senior Unsecured Notes mature on December 15, 2025. Interest on the 5.75% Senior Unsecured Notes is to be paid semi-annually on February 15 and August 15, commencing August 15, 2018, at an annual rate of 5.75% . The indenture relating to the 5.75% Senior Unsecured Notes contained various limitations on the Borrower’s and its restricted subsidiaries’ ability to incur additional indebtedness, pay dividends or repay certain debt, make loans and investments, sell assets, create liens, enter into transactions with affiliates, enter into agreements restricting the Borrower’s subsidiaries ability to pay dividends, and merge and consolidate with other companies, among other things. No principal payments are required with respect to the Senior Secured Notes prior to their final maturity. The obligations of the Borrower under the 5.75% Senior Unsecured Notes and the related indenture are guaranteed by its U.S. subsidiary guarantors that guarantee the New Term Loan Facility. The obligations of the Company under the 5.75% Senior Unsecured Notes and the indenture are unsecured. If any Event of Default (other than a default relating to certain events of bankruptcy or insolvency of PQ Corporation or certain of its subsidiaries) occurs and is continuing under the Indenture, the Trustee or the Holders of at least 30% in principal amount of the then total outstanding notes by notice to the Company may declare the principal, premium, if any, interest and any other monetary obligations on all the then outstanding notes to be due and payable immediately. If an event of default arising from certain events of bankruptcy or insolvency of the Company occurs, the principal of, premium, if any, and interest on all the Senior Secured Notes shall become immediately due and payable without any declaration or other act on the part of the trustee or any holders. At any time prior to December 15, 2020, the Borrower may, at its option and on one more occasions, redeem (a) up to 40% of the aggregate principal amount of the 5.75% Senior Unsecured Notes with the cash proceeds from certain equity offerings at a redemption price equal to the sum of 105.75% of the aggregate principal amount thereof plus accrued and unpaid interest thereon, and (b) all or part of the 5.75% Senior Unsecured Notes at 100.00% of the aggregate principal amount redeemed plus accrued and unpaid interest thereon and a make-whole premium (the “Applicable Premium”). The Applicable Premium is equal to the greater of: (a) 1% of the principal amount of notes redeemed, or (b) the excess, if any, of: (1) the present value at the redemption date of (i) the redemption price of such notes at December 15, 2020 (as set forth in the table below), plus (ii) all required remaining scheduled interest payments due on such notes through December 15, 2020 (excluding accrued but unpaid interest to, but excluding, the redemption date), computed using a discount rate equal to the applicable United States Treasury rate as of such redemption date plus 50 basis points; over (2) the outstanding principal amount of such notes on the redemption date. On or after December 15, 2020, the 5.75% Senior Unsecured Notes are redeemable, in whole or in part, at the redemption prices (expressed as percentages of principal amount of the 5.75% Senior Unsecured Notes to be redeemed) set forth below, plus accrued and unpaid interest, if any, to, but not including, the redemption date, if redeemed on or after any of the dates below until the subsequent date below: Year Percentage December 15, 2020 102.875% December 15, 2021 101.438% December 15, 2022 and thereafter 100.000% Upon the occurrence of a change of control, as defined, each holder will have the right to require the Company to purchase all or any part of such holder’s Senior Secured Notes at a purchase price in cash equal to 101% of the principal amount, plus accrued and unpaid interest. Other Debt New Markets Tax Credit Financing On October 24, 2013, PQ Holdings’ (and now the Company’s) subsidiary Potters Industries, LLC (“Potters”) entered into a NMTC financing arrangement with JPMorgan Chase Bank N.A. and several of its affiliates (“Chase”) and TX CDE V LLC, an affiliate of Texas LIC Development Company LLC d/b/a Texas Community Development Capital (“TX CDE”) to fund the expansion of Potters’ manufacturing facility in Paris, Texas (the “2013 NMTC Agreement”). The NMTC program, which is administered by the United States Treasury Department, requires certain balance sheet commitments. The 2013 NMTC Agreement will provide the Company with certain monetary benefits as an offset to specifically identified capital expenditures. The 2013 NMTC Agreement requires that certain commitments and covenants be maintained over a period of seven years in order to legally recognize the benefit. Chase agreed to contribute $6,634 and an additional $15,632 in funds lent to Chase by Potters Holdings II, L.P. to TX CDE. TX CDE, in turn, lent $21,000 in the form of $5,368 and $15,632 of notes to Potters, which used the proceeds to finance the expansion of Potters’ manufacturing facility in Paris, Texas. The capital expenditures associated with the 2013 NMTC Agreement were completed in 2014. The $21,000 of debt related to the 2013 NMTC was assumed as part of the Business Combination and was outstanding as of December 31, 2018 . On May 17, 2016, Potters entered into a NMTC financing arrangement with U.S. Bank N.A. and several of its affiliates (“USB”) and MRC XX LLC, an affiliate of Midwest Renewable Capital, LLC (“MRC”), to fund the expansion of Potters’ manufacturing facility in Augusta, Georgia (the “May 2016 NMTC Agreement”). The May 2016 NMTC Agreement provides the Company with certain monetary benefits as an offset to specifically identified capital expenditures. The May 2016 NMTC Agreement requires that certain commitments and covenants be maintained over a period of seven years in order to legally recognize the benefit. USB agreed to contribute $3,732 and an additional $7,822 in funds lent to USB by Potters Holdings II, L.P. to MRC. MRC, in turn, lent $11,000 in the form of $7,823 , $1,311 and $1,866 of notes to Potters, which used the proceeds to finance the expansion of Potters’ manufacturing facility in Augusta, Georgia. The $11,000 was outstanding as of December 31, 2018 . The capital expenditures associated with the May 2016 NMTC Agreement were completed in 2017. On December 29, 2016, Potters entered into a second NMTC financing arrangement with USB and MRC whereby USB agreed to contribute $3,815 and an additional $7,775 in funds lent to USB by Potters Holdings II, L.P. to MRC. MRC, in turn, lent $11,000 in the form of $7,775 , $1,402 and $1,823 of notes to Potters, which will use the proceeds as working capital for another expansion of Potters’ manufacturing facility in Paris, Texas (the “December 2016 NMTC Agreement”). The $11,000 was outstanding as of December 31, 2018 . Potters expended the proceeds of the notes as working capital in 2017. On June 22, 2017, Potters, entered into a NMTC financing arrangement with U.S. Bank N.A. (“USB”), one of USB’s affiliates (“USB Investment Fund”) and Business Conduit No. 28, LLC, an affiliate of Community Reinvestment Fund, Inc. (“CRF”). USB contributed $3,054 to USB Investment Fund, and Potters Leveraged Lender LLC, an indirect subsidiary of the Company, lent USB Investment Fund $6,221 . USB Investment Fund then contributed $9,000 to CRF, which in turn lent $8,820 to Potters pursuant to a credit agreement (the “June 2017 NMTC Agreement”). Potters used the $8,820 in proceeds to acquire equipment for the expansion of Potters’ manufacturing facility in Paris, Texas. The June 2017 NMTC Agreement provides the Company with certain monetary benefits as an offset to specifically identified capital expenditures. The June 2017 NMTC Agreement requires that certain commitments and covenants are maintained over a period of seven years in order to legally recognize the benefit. The $8,820 was outstanding as of December 31, 2018 . The capital expenditures associated with the June 2017 NMTC Agreement were completed in 2018. In connection with the aforementioned NMTC financing arrangements, the Company provided indemnifications related to its actions or inactions which cause either a NMTC disallowance or recapture event. In the event that the Company causes either a recapture or disallowance of the tax credits expected to be generated under this program, then the Company will be required to repay the disallowed or recaptured tax credits plus an amount sufficient to pay the taxes on such repayment to the counterparty of the agreement. This indemnification covers the Company’s actions and inactions prior the end of the seven-year term of each agreement. The maximum potential amount of future payments under this indemnification is approximately $24,649 . The Company currently believes that the likelihood of a required payment under this indemnification is remote. Sovitec Credit Line On June 12, 2017, the Company acquired Sovitec and assumed its obligations to Belfius Bank NV (“Belfius”). On June 8, 2017, Sovitec entered into a credit agreement with Belfius governing a €14,500 credit line which is divided into four tranches. Tranche A was issued in the amount of €7,500 in the form of a Euro roll-over credit with a maturity date of December 31, 2021. Tranche B was issued in the amount of €3,000 in the form of a Euro roll-over credit with a full principal payment due on its maturity date of September 30, 2022. A working capital line of credit (“Working Capital”) of €3,000 was issued under the form of straight loans with a maturity date up to 90 days after borrowings are made on the line. A capital expenditure line of credit (“CAPEX line”) of €1,000 was issued under the form of straight loans with a maturity date of September 30, 2021. Tranche A is subject to principal payments of €750 made on September 30 and December 31 of each year. Borrowings under the credit agreement bear rates based on Sovitec’s ratio of net debt to Normalized EBITDA. Normalized EBITDA is defined as the Sovitec consolidated operating profit before non-recurring items (i.e. items non-related to normal operations of the last twelve month period and provided an acceptable description of the one-off character of those items is given) and before taxation, depreciation and amortization. Interest rate margins are subject to being reset on June 30 of each year. Interest rates reset based on three net debt to Normalized EBITDA ratio ranges of less than 2, between 2 and 3 or greater than 3. Rates for each tranche of debt reset based on 1 to 9 month EURIBOR rates (not lower than zero) plus a margin that can range between 1.10% to 1.55% for Tranche A, 1.85% to 2.15% for Tranche B, 0.90% and 1.20% for Working Capital and 1.25% and 1.80% for the CAPEX line. As of December 31, 2018 , the interest rate on the credit agreements are as follows: Tranche A, 1.10% , Tranche B, 1.85% , Working Capital, 0.90% and CAPEX 1.25% . As of December 31, 2018 , the following principal balances are outstanding on each debt instrument: Tranche A, $5,148 , Tranche B, $3,433 , Working Capital, $1,945 and CAPEX $1,144 . Loans and guarantees under the credit agreement are secured by (1) a first priority security interest on the Sovitec properties located Fleurus, Belgium and Florange, France and (2) 100% of the nominative shares in Sovitec’s wholly owned parent company, Sovitec International B.V. The credit agreement contains various non-financial and financial covenants. Each limits the ability of Sovitec and its restricted subsidiaries to incur certain indebtedness or liens, merge, consolidated or liquidate, dispose of certain property, make investments or declare or pay dividends. The credit agreement also contains one financial covenant which requires maintaining a maximum net debt/EBITDA ratio of 3 :1 during the first three years of the agreement and afterwards a maximum 2.5 :1 ratio. The Company is in compliance with all debt covenants as of December 31, 2018 . Notes Payable The Company also has several note payable agreements denominated in Japanese Yen which enables the Company to borrow up to a total of 260,000 Japanese Yen, or $2,358 . Borrowings bear interest at either TIBOR (“Tokyo Interbank Offered Rate”) plus a margin or the short-term prime rate. The terms of the agreements vary and are renewable upon expiration of the term with the balances due in 2019 . Borrowings under the agreement are payable at the option of the Company throughout the term of the agreements. Borrowings outstanding under these agreements were $2,358 and $2,306 as of December 31, 2018 and 2017 , respectively. Certain of the Company’s foreign subsidiaries maintain other note payable agreements. These agreements are not further described as they are not significant to the consolidated financial statements. Fair Value of Debt The fair value of a financial instrument is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants. As of December 31, 2018 and 2017 , the

Other Long-term Liabilities

Other Long-term Liabilities	12 Months Ended
	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
Other Long-term Liabilities	17. Other Long-term Liabilities: The following table summarizes the components of other long-term liabilities as follows: December 31, 2018 2017 Pension benefits $ 75,430 $ 69,914 Supply contract (see Note 25) — 20,612 Other postretirement benefits 3,233 4,051 Supplemental retirement plans 10,763 11,667 Reserve for uncertain tax positions 3,176 4,244 Asset retirement obligation 4,224 4,094 Other 7,999 5,889 $ 104,825 $ 120,471

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Financial Instruments	18. Financial Instruments: The Company uses (1) interest rate related derivative instruments to manage its exposure related to changes in interest rates on its variable-rate debt instruments (2) commodity derivatives to manage its exposure to commodity price fluctuations, and (3) foreign currency related derivative instruments to manage its foreign currency exposure to its net investments in certain foreign operations. The Company does not speculate using derivative instruments. By using derivative financial instruments to hedge exposures to changes in interest rates, commodity prices and foreign currency, the Company exposes itself to credit risk and market risk. Credit risk is the failure of the counterparty to perform under the terms of the derivative contract. When the fair value of a derivative contract is an asset, the counterparty owes the Company, which creates credit risk for the Company. When the fair value of a derivative contract is a liability, the Company owes the counterparty and, therefore, the Company is not exposed to the counterparty’s credit risk in those circumstances. The Company minimizes counterparty credit risk in derivative instruments by entering into transactions with high quality counterparties. The derivative instruments entered into by the Company do not contain credit-risk-related contingent features. Market risk is the adverse effect on the value of a derivative instrument that results from a change in interest rates, currency exchange rates or commodity prices. The market risk associated with interest rate and commodity price contracts is managed by establishing and monitoring parameters that limit the types and degree of market risk that may be undertaken. Use of Derivative Financial Instruments to Manage Commodity Price Risk. The Company is exposed to risks in energy costs due to fluctuations in energy prices, particularly natural gas. The Company has a hedging program in the United States which allows the Company to mitigate exposure to natural gas volatility with natural gas swap agreements. Fair value is determined based on estimated amounts that would be received or paid to terminate the contracts at the reporting date based on quoted market prices of comparable contracts. The respective current and non-current liabilities are recorded in accrued liabilities and other long-term liabilities and the respective current and non-current assets are recorded in prepaid and other current assets and other long-term assets, as applicable, in the Company’s consolidated balance sheet. As the derivatives are designated and qualify as cash-flow hedges, the gains or losses on the natural gas swaps are recorded in stockholders’ equity as a component of other comprehensive income (loss) (“OCI”), net of tax. Reclassifications of the gains and losses on natural gas hedges into earnings are included in production cost and subsequently charged to cost of goods sold in the consolidated statements of operations in the period in which the associated inventory is sold. As of December 31, 2018 , the Company’s natural gas swaps had a remaining notional quantity of 3.9 million MMBTU to mitigate commodity price volatility through December 2021. Use of Derivative Financial Instruments to Manage Interest Rate Risk. The Company is exposed to fluctuations in interest rates on its senior secured credit facilities. Changes in interest rates will not affect the market value of such debt but will affect the amount of the Company’s interest payments over the term of the loans. Likewise, an increase in interest rates could have a material impact on the Company’s cash flow. The Company hedges the interest rate fluctuations on debt obligations through interest rate cap agreements. The Company records these agreements at fair value as assets or liabilities in its consolidated balance sheet. As the derivatives are designated and qualify as cash flow hedges, the gains or losses on the interest rate cap agreements are recorded in stockholders’ equity as a component of OCI, net of tax. Reclassifications of the gains and losses on the interest rate cap agreements into earnings are recorded as part of interest expense in the consolidated statements of operations as the Company makes its interest payments on the hedged portion of its senior secured credit facilities. Fair value is determined based on estimated amounts that would be received or paid to terminate the contracts at the reporting date based on quoted market prices. In July 2016, the Company entered into interest rate cap agreements, paying a premium of $1,551 to mitigate interest rate volatility from July 2016 through July 2020 by employing varying cap rates, ranging from 1.50% to 3.00% on $1,000,000 of notional variable-rate debt. The cap rate in effect at December 31, 2018 was 2.50% . In November 2018, the Company entered into additional interest rate cap agreements to mitigate interest rate volatility from July 2020 through July 2022, with a cap rate of 3.50% on $500,000 of notional variable-rate debt. Use of Derivative Financial Instruments to Manage Foreign Currency Risk. The Company is exposed to risks related to its net investments in foreign operations due to fluctuations in foreign currency exchange rates, particularly between the United States dollar and the Euro. In connection with the February 2018 term loan refinancing (see Note 16 to these consolidated financial statements), the Company entered into multiple cross currency interest rate swap arrangements with an aggregate notional amount of €280,000 ( $320,404 as of December 31, 2018 ) to hedge this exposure on the net investments of certain of its Euro-denominated subsidiaries. The Company records these swap agreements at fair value as assets or liabilities in its consolidated balance sheet. As the derivatives are designated and qualify as net investment hedges, changes in the fair value of the swaps attributable to changes in the spot exchange rates are recognized in cumulative translation adjustment (“CTA”) within OCI and are held there until the hedged net investments are sold or substantially liquidated. Changes in the fair value of the swaps attributable to the cross currency basis spread are excluded from the assessment of hedge effectiveness and are recorded in current period earnings. Upon such sale or liquidation, the amount recognized in CTA is reclassified to earnings and reported in the same line item as the gain or loss on the liquidation of the net investments. The fair values of derivative instruments held as of December 31, 2018 and 2017 are shown below: December 31, Balance sheet location 2018 2017 Derivative assets: Derivatives designated as cash flow hedges: Natural gas swaps Prepaid and other current assets $ 21 $ — Interest rate caps Prepaid and other current assets 1,358 44 Interest rate caps Other long-term assets 546 999 1,925 1,043 Derivatives designed as net investment hedges: Cross currency swaps Prepaid and other current assets 5,499 — Cross currency swaps Other long-term assets 13,344 — 18,843 — Total derivative assets $ 20,768 $ 1,043 Derivative liabilities: Derivatives designated as cash flow hedges: Natural gas swaps Accrued liabilities $ 36 $ 318 Natural gas swaps Other long-term liabilities 148 130 Interest rate caps Other long-term liabilities 1,842 — Total derivative liabilities $ 2,026 $ 448 The following table shows the effect of the Company’s derivative instruments designated as hedges on accumulated other comprehensive income (loss) (“AOCI”) and the statements of operations for the years ended December 31, 2018 , 2017 and 2016 : Years ended December 31, 2018 2017 2016 Location of gain (loss) reclassified from AOCI into income Amount of gain (loss) recognized in OCI on derivatives Amount of gain (loss) reclassified from AOCI into income Amount of gain (loss) recognized in OCI on derivatives Amount of gain (loss) reclassified from AOCI into income Amount of gain (loss) recognized in OCI on derivatives Amount of gain (loss) reclassified from AOCI into income Interest rate caps Interest (expense) income $ (981 ) $ (256 ) $ (4,760 ) $ (40 ) $ 4,250 $ — Natural gas swaps Cost of goods sold $ 637 $ 353 $ (1,300 ) $ (222 ) $ (802 ) $ (1,433 ) $ (344 ) $ 97 $ (6,060 ) $ (262 ) $ 3,448 $ (1,433 ) The following table shows the effect of the Company’s cash flow hedge accounting on the consolidated statements of operations for the years ended December 31, 2018 , 2017 and 2016 : Location and amount of gain (loss) recognized in income on cash flow hedging relationships Years ended December 31, 2018 2017 2016 Cost of goods sold Interest (expense) income Cost of goods sold Interest (expense) income Cost of goods sold Interest (expense) income Total amounts of income and expense line items presented in the statement of operations in which the effects of cash flow hedges are recorded $ (1,226,520 ) $ (113,723 ) $ (1,095,265 ) $ (179,044 ) $ (810,085 ) $ (140,315 ) The effects of cash flow hedging: Gain (loss) on cash flow hedging relationships: Interest contracts: Amount of gain (loss) reclassified from AOCI into income — (256 ) — (40 ) — — Commodity contracts: Amount of gain (loss) reclassified from AOCI into income 353 — (222 ) — (1,433 ) — The following table shows the effect of the Company’s net investment hedges on AOCI and the consolidated statements of operations for the years ended December 31, 2018 , 2017 and 2016 : Amount of gain (loss) recognized in OCI on derivative Location of (gain) loss reclassified from AOCI into income Amount of (gain) loss reclassified from AOCI into income Location of gain (loss) recognized in income on derivative (amount excluded from effectiveness testing) Amount of gain (loss) recognized in income on derivative (amount excluded from effectiveness testing) Years ended December 31, Years ended December 31, Years ended December 31, 2018 2017 2016 2018 2017 2016 2018 2017 2016 Cross currency swaps $ 18,843 $ — $ — (Gain) loss on sale of subsidiary $ — $ — $ — Interest (expense) income $ 7,898 $ — $ — Amounts of unrealized losses in AOCI that are expected to be reclassified to the consolidated statement of operations over the next twelve months are $ 640 as of December 31, 2018 .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	19. Income Taxes: The Tax Cuts and Jobs Act (the “TCJA”) was enacted on December 22, 2017 and certain provisions became effective January 1, 2018. The TCJA imposed significant changes to U.S. tax law, such as lowering U.S. corporate income tax rates, implementing a territorial tax system and levying a one-time transition tax on deemed repatriated earnings of foreign subsidiaries. In response to the TCJA, the SEC staff issued Staff Accounting Bulletin No. 118 (“SAB 118”) to address the application of U.S. GAAP in situations when a registrant did not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the TCJA. As amounts were refined, SAB 118 allowed registrants to record provisional adjustments during a measurement period that extended beyond one year of the TCJA enactment date. In accordance with SAB 118, the Company has finalized the impacts of the transition tax as of December 31, 2018 and has recorded a measurement period adjustment of $2,102 as a benefit to tax expense. There was no cash tax outlay associated with the final transition tax amount, as the Company elected to utilize NOL carryforwards to offset the associated taxable income. The TCJA also established other new provisions that became effective in 2018 . These include, but are not limited to, (1) a new provision designed to tax low-taxed income of foreign subsidiaries (i.e., “GILTI”), which allows for the possibility of using foreign tax credits ("FTCs") and a deduction of up to 50% to offset any resulting income tax liability (subject to some limitations); (2) limitations on the deductibility of certain executive compensation (“162(m)”); (3) limitations on the deductibility of interest expense (“163(j)”); and (4) limitations on the use of FTCs to reduce the U.S. income tax liability. While many of these provisions are expected to have an impact on the Company’s tax expense and deferred taxes for the year ended December 31, 2018 and future periods, the Company expects the GILTI provisions and 163(j) to have the most significant impact. While significant additional guidance regarding U.S. tax reform has been put forth during the year ended December 31, 2018 , at this time the overall impact of the TCJA on the Company’s future income tax provision continues to remain uncertain. With respect to GILTI, the Company has experienced significant impact to tax expense for the year ended December 31, 2018 because of its substantial U.S. NOL balance and being unable to avail itself of both U.S. foreign tax credits and the GILTI special deduction (“Section 250 Deduction”). The December 31, 2018 impact to tax expense with respect to GILTI is $15,444 . Based on FASB guidance, the Company is permitted to make an accounting policy election to either (1) treat the taxes incurred as a result of the GILTI provision as a current-period expense when incurred or (2) factor such amounts into its measurement of deferred taxes. The Company has elected to treat any expense incurred as a current-period expense. With respect to 163(j), the Company has experienced a significant disallowance with respect to its current year interest expense. The Company’s 163(j) interest disallowance is $57,705 for the year ended December 31, 2018 . This disallowance has no impact to overall tax expense, given that any disallowed interest deductions are permitted to be carried forward indefinitely and, as such, are set up as deferred tax assets. The Company has evaluated the realizability of this deferred tax asset, and believes it is more-likely-than-not that it will be realized, using reversal of existing taxable temporary differences. Income (loss) before income taxes and noncontrolling interest within or outside the United States are shown below: Years ended 2018 2017 2016 Domestic $ 3,935 $ (137,147 ) $ (84,094 ) Foreign 84,681 76,513 14,977 Total $ 88,616 $ (60,634 ) $ (69,117 ) The provision (benefit) for income taxes as shown in the accompanying consolidated statements of operations consists of the following: Years ended 2018 2017 2016 Current: Federal $ — $ — $ — State 2,470 806 91 Foreign 23,080 20,209 10,088 25,550 21,015 10,179 Deferred: Federal 12,854 (135,970 ) 8,654 State (784 ) (1,817 ) 292 Foreign (8,625 ) (2,425 ) (9,084 ) 3,445 (140,212 ) (138 ) Provision (benefit) for income taxes $ 28,995 $ (119,197 ) $ 10,041 A reconciliation of income tax expense (benefit) at the U.S. federal statutory income tax rate to actual income tax expense is as follows: Years ended 2018 2017 2016 Tax at statutory rate $ 18,610 $ (21,222 ) $ (24,191 ) State income taxes, net of federal income tax benefit 1,203 (7,754 ) (4,110 ) Repatriation of non-US earnings 14,187 (24,912 ) 4,576 Change in tax status-Eco Services-Passthrough to C-Corporation — — 33,891 Changes in uncertain tax positions (996 ) 974 (2,383 ) Change in valuation allowances 5,075 6,771 2,577 Rate changes (4,016 ) (63,319 ) — Change in state effective rates 691 (340 ) (290 ) Foreign withholding taxes 1,828 978 1,505 Foreign tax rate differential 2,191 (13,634 ) (3,040 ) Non-deductible transaction costs 84 1,679 667 Permanent difference created by foreign exchange gain or loss (7,550 ) 3,503 1,686 Research and development tax credits (1,173 ) — — Other, net (1,139 ) (1,921 ) (847 ) Provision (benefit) for income taxes $ 28,995 $ (119,197 ) $ 10,041 The total tax provision (benefit) of $28,995 , $(119,197) and $10,041 for the years ended December 31, 2018 , 2017 and 2016 , respectively, on the Company’s consolidated pre-tax income (loss) for the period differs from the U.S. statutory tax rate of 21% . This difference is principally due to the impacts of U.S. tax reform (including GILTI), the effect of permanent differences related to foreign currency exchange gain or loss, foreign income tax in jurisdictions with statutory rates different than the U.S. rate, state taxes, non-deductible transaction costs, foreign withholding taxes, changes in valuation allowance, and changes in uncertain tax positions. Prior to the Business Combination on May 4, 2016, Eco Services was a single member limited liability company and taxed as a partnership for federal and state income tax purposes. As such, all income tax liabilities and/or benefits of Eco Services were passed through to their members. Because Eco Services was taxed as a partnership, it did not record deferred taxes on the basis difference on their financial statements. Following the Business Combination on May 4, 2016, Eco Services had a change in tax status and is now taxed as a C-Corporation subject to federal and state corporate level income taxes at prevailing corporate tax rates. As Eco Services had not previously recorded deferred taxes on the basis difference, the Company recognized net deferred tax liabilities of $33,891 for the year ended December 31, 2016 primarily related to basis differences in depreciable fixed assets and intangible assets based upon prevailing corporate tax rates. Deferred incomes taxes reflect the net tax effects of temporary differences between the financial statement carrying amounts of assets and liabilities and the amounts recognized for income tax purposes. U.S. GAAP requires that deferred tax assets and liabilities are measured using enacted tax rates expected to be applied to taxable income in the years in which those temporary differences are expected to reverse in the future. As a result of the reduction in the U.S. corporate income tax rate from 35% to 21% , the Company was required to remeasure existing deferred tax balances using the new U.S. statutory tax rate in 2017. Deferred tax assets (liabilities) are comprised of the following: December 31, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 116,607 $ 144,267 Section 163j interest disallowance carryforward 13,387 — Pension 16,397 16,255 Post retirement health 1,385 561 Transaction costs 708 1,183 Natural gas contracts and interest rate swaps 335 225 Unrealized translation losses 3,737 5,065 US research and development credits 1,173 — Other 38,855 38,290 Valuation allowance (48,711 ) (64,945 ) $ 143,873 $ 140,901 Deferred tax liabilities: Depreciation $ (92,911 ) $ (86,532 ) Undistributed earnings of non-US subsidiaries (6,648 ) (8,334 ) Inventory (10,432 ) (11,324 ) Intangible assets (174,327 ) (184,937 ) Cross currency swaps (4,654 ) — Other (32,230 ) (36,810 ) $ (321,202 ) $ (327,937 ) Net deferred tax liabilities $ (177,329 ) $ (187,036 ) Included in the 2018 and 2017 deferred tax asset and liability amounts for depreciation, intangible assets, inventory, natural gas contracts, unrealized transaction losses, and other above is $45,251 and $45,873 , respectively, of a net deferred tax liability related to the Company’s investment in Potters, which is a partnership for federal income tax purposes. The Company and one of its subsidiaries own in aggregate 100% of Potters and the assets and liabilities of Potters are included in the consolidated financial statements of the Company. The $177,329 in net deferred tax liabilities as of December 31, 2018 consists of $18,795 in non-current deferred tax assets and $196,124 in net non-current deferred tax liabilities. The $187,036 in net deferred tax liabilities as of December 31, 2017 consists of $2,300 in non-current deferred tax assets and $189,336 in net non-current deferred tax liabilities. The change in net deferred tax liabilities for the years ended December 31, 2018 and 2017 was primarily related to the decrease in deferred tax liabilities resulting from the revaluing of domestic deferred tax amounts, pursuant to U.S. tax reform lowering the statutory tax rate, establishing a deferred tax asset with respect to 163(j), as well as the change in book amortization of intangibles with no corresponding tax basis and movement in valuation allowances with respect to acquired Sovitec entities. The following are changes in the deferred tax valuation allowance during the years ended December 31, 2018 and 2017 : Years ended 2018 2017 Beginning Balance $ 64,945 $ 38,271 Additions 5,314 34,863 Reductions (21,548 ) (8,189 ) Ending Balance $ 48,711 $ 64,945 Included in the additions line above is $20,753 related to fair value adjustments recorded to goodwill as part of the initial Acquisition purchase accounting analysis for the year ended December 31, 2017 . Included in the reductions line above is $20,038 related to fair value adjustments recorded to goodwill as part of the finalization of the Acquisition purchase accounting for the year ended December 31, 2018 . The net change in the total valuation allowance was a decrease of $16,234 in 2018 . The valuation allowance at December 31, 2018 was primarily related to foreign and state net operating loss carryforwards and tax credits that, in the judgment of management, are not more likely than not to be realized. In assessing the ability to realize deferred tax assets, management considered whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considered the scheduled reversal of deferred tax liabilities (including the impact of available carryback and carryforward periods), projected future taxable income, and tax-planning strategies that are prudent in making this assessment. In order to fully realize deferred tax assets, the Company will need to generate future taxable income prior to the expiration of the net operating loss and credit carryforwards. The amount of the deferred tax assets considered realizable, however, could be reduced in the near term if estimates of future taxable income during the carryforward period are reduced. Management considered certain earnings in non-U.S. subsidiaries to be available for repatriation in the future. The tax cost associated with non-U.S. subsidiary earnings and distributions for the year ended December 31, 2018 has been recorded as tax expense for the period. In this regard the Company expects to deduct, rather than credit, foreign tax expense in computing the U.S. tax effects of repatriation from non-U.S. subsidiaries in 2018 . The unremitted earnings of non-U.S. subsidiaries and affiliates that have not been permanently reinvested amount to $168,304 and $210,979 as of December 31, 2018 and 2017 , respectively. The deferred foreign withholding tax liability on these undistributed earnings is estimated to be $6,648 and $8,334 as of December 31, 2018 and 2017 , respectively. As a result of U.S. tax reform, the liability on unremitted earnings as of December 31, 2018 is only related to foreign withholding taxes, as all earnings and profits were deemed to be repatriated for U.S. income tax purposes as a result of U.S. Tax Reform. The cumulative unremitted earnings of foreign subsidiaries outside the United States in excess of the $168,304 are considered permanently reinvested, for which no withholding taxes have been provided. Such earnings are expected to be reinvested indefinitely and, as a result, no deferred tax liability has been recognized with regard to such earnings. Determination of the deferred withholding tax liability on these unremitted earnings is not practicable, principally because such liability, if any, is dependent on circumstances existing if and when remittance occurs. The following table summarizes the activity related to the Company’s gross unrecognized tax benefits: Years ended 2018 2017 Balance at beginning of period $ 11,431 $ 16,128 Increases related to prior year tax positions — 68 Decreases related to prior year tax positions (1,538 ) (5,508 ) Increases related to current year tax positions 282 743 Balance at end of period $ 10,175 $ 11,431 The total unrecognized tax benefits of $10,175 and $11,431 were generated from legacy PQ Corporation. If these amounts are recognized in future periods, it would affect the effective tax rate on income from continuing operations for the years in which they are recognized. Interest and penalties recognized related to uncertain tax positions amounted to $42 and $52 for the years ended December 31, 2018 and 2017 , respectively. To the extent interest and penalties are not assessed with respect to uncertain tax positions, amounts accrued will be reduced and reflected as a reduction of the overall income tax provision in the period for which the event occurs requiring the adjustment. The $1,088 and $1,270 in accrued interest and penalties as of December 31, 2018 and 2017 , respectively, is recorded in other long-term liabilities on the consolidated balance sheets. Due to the Business Combination, the Company files numerous consolidated and separate income tax returns in the U.S. federal jurisdiction and in many state and foreign jurisdictions. The following describes the open tax years, by major tax jurisdiction, as of December 31, 2018 : Jurisdiction Period United States-Federal 2007-Present United States-State 2007-Present Canada (1) 2010-Present Germany 2015-Present Netherlands 2012-Present Mexico 2014-Present United Kingdom 2012-Present Brazil 2014-Present (1) Includes federal as well as local jurisdictions Given that certain U.S. companies have net operating loss carryforwards, the statute for examination by taxing authorities in the United States, and certain state jurisdictions, will remain open for a period following the use of such net operating loss carryforwards, extending the period for examination beyond the years indicated above. The Company has subsidiaries in various states, provinces and countries that are currently under audit for years ranging from 2007 through 2017. To date, no material adjustments have been proposed as a result of these audits. As of December 31, 2018 , the Company does not believe that there are any positions for which it is reasonably possible that the total amount of unrecognized tax benefits will significantly increase or decrease within the next 12 months. The Company has a NOL available of $284,237 to reduce future federal taxes payable. The current federal carry-forward period for those NOL’s is 20 years because they were generated prior to U.S. tax reform being enacted. In light of tax reform, any net operating losses incurred after December 31, 2017 will be allowed to carry forward indefinitely. As a result of the 2014 change in control, $144,357 of the $284,237 are subject to the limitations of Section 382 of the Internal Revenue Code (“IRC”). Although subject to the limitations of IRC §382, management believes it is more likely than not that the Company will realize the entire $144,357 in pre-transaction NOLs in future years. The remaining $139,880 relates to periods after the 2014 change in control and would not be subject to limitation under IRC §382. For state income tax purposes, the Company incurred net operating losses of $21,594 for 2018 that may be carried forward at a minimum period of 5 years , and in certain circumstances indefinitely, among the states in which the Company is subject to tax to reduce future state income taxes payable. Cumulative state net operating losses carrying forward into 2019 are $681,010 . A valuation allowance of $17,718 has been applied against the total $33,179 of state net operating loss deferred tax assets, leaving losses of $15,461 that have been recognized for financial accounting purposes for the portion of those losses that the Company believes, on a more likely than not basis, will be realized. Foreign net operating losses of $131,453 , of which $586 will begin to expire in 2019, $2,205 will begin to expire in 2026, $92 will begin to expire in 2028, $7,616 will begin to expire in 2029 with the remaining $120,954 carrying forward indefinitely, are available to reduce future foreign income taxes payable. A valuation allowance of $11,940 has been applied to $31,431 of deferred tax assets related to foreign net operating loss carry-forwards, leaving a net deferred tax asset relating to foreign net operating losses of $19,491 that has been recognized for financial accounting purposes. Cash payments for income taxes, net of refunds, are as follows: Years ended 2018 2017 2016 Domestic $ 2,160 $ 1,647 $ 373 Foreign 21,682 27,552 16,608 $ 23,842 $ 29,199 $ 16,981

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Benefit Plans	20. Benefit Plans: The Company sponsors defined benefit pension plans covering employees in the United States and certain employees at its foreign subsidiaries. Benefits for a majority of the plans are based on average final pay and years of service. The Company’s funding policy is to fund the minimum required contribution under local statutory requirements. The Company sponsors unfunded plans to provide certain health care benefits to retired employees in the United States and Canada. The plans pay a stated percentage of medical expenses reduced by deductibles and other coverage. The plans are unfunded and obligations are paid out of the Company’s operations. The Company also has defined benefit supplementary retirement plans which provide benefits for certain U.S. employees in excess of qualified plan limitations. The obligations are paid out of the Company’s general assets, including assets held in a Rabbi trust, or restoration plan assets. The Company uses a December 31 measurement date for all of its defined benefit pension, postretirement medical and supplementary retirement plans. The following discussion includes information for the Eco Services benefit plans for all periods presented, and the acquired PQ Holdings benefit plans beginning on the date of the Business Combination. The Eco Services benefit plans include two defined benefit pension plans and one retiree health plan, all based in the U.S. The PQ Holdings benefit plans include a U.S. defined benefit pension plan as well as the defined benefit pension plans for all of the Company’s foreign subsidiaries, two retiree health plans (one each in the U.S and Canada), and the Company’s defined benefit supplementary retirement plans. Of the Company’s three defined benefit pension plans covering employees in the U.S., only the Eco Services Hourly Pension Plan continues to accrue benefits for certain participants. All future accruals were frozen for the PQ Corporation Retirement Plan as of December 31, 2006 and for the Eco Services Pension Equity Plan as of December 31, 2016. With respect to the Company’s three retiree health plans, the PQ Holdings plans in the U.S. and Canada were closed to new retirees as of December 31, 2006. The Eco Services Postretirement Life and Dental Plan was closed to new retirees effective July 1, 2017. The Company’s defined benefit supplementary retirement plans were frozen to future accruals as of December 31, 2006. Defined Benefit Pension Plans The following tables summarize changes in the benefit obligation, plan assets and funded status of the Company’s significant defined benefit pension plans as well as the components of net periodic benefit cost, including key assumptions: U.S. Foreign December 31, December 31, 2018 2017 2018 2017 Change in benefit obligation: Benefit obligation at beginning of period $ 261,102 $ 247,418 $ 119,710 $ 106,025 Service cost 1,019 1,219 3,566 3,686 Interest cost 9,599 10,115 3,340 3,271 Participant contributions — — 570 493 Plan amendments — — 179 — Plan curtailments (952 ) — (340 ) — Plan settlements — (2,264 ) (1,071 ) — Benefits paid (11,453 ) (9,591 ) (2,569 ) (2,967 ) Expenses paid — — (363 ) (319 ) Net transfer in — — 1,535 — Actuarial (gains) losses (13,004 ) 14,205 (5,432 ) (2,169 ) Translation adjustment — — (7,022 ) 11,690 Benefit obligation at end of the period $ 246,311 $ 261,102 $ 112,103 $ 119,710 Change in plan assets: Fair value of plan assets at beginning of period $ 218,374 $ 198,915 $ 96,518 $ 86,145 Actual return on plan assets (12,854 ) 27,554 (540 ) 217 Employer contributions 1,688 3,760 4,249 3,781 Employee contributions — — 570 493 Plan settlements — (2,264 ) (1,071 ) — Benefits paid (11,453 ) (9,591 ) (2,569 ) (2,967 ) Expenses paid — — (363 ) (319 ) Acquisitions — — 1,013 — Translation adjustment — — (6,020 ) 9,168 Fair value of plan assets at end of the period $ 195,755 $ 218,374 $ 91,787 $ 96,518 Funded status of the plans (underfunded) $ (50,556 ) $ (42,728 ) $ (20,316 ) $ (23,192 ) Amounts recognized in the consolidated balance sheets consist of: U.S. Foreign December 31, December 31, 2018 2017 2018 2017 Noncurrent asset $ — $ — $ 4,670 $ 3,503 Current liability — — (748 ) (673 ) Noncurrent liability (50,556 ) (42,728 ) (24,238 ) (26,022 ) Accumulated other comprehensive income (loss) 1,218 10,499 (1,829 ) (2,871 ) Net amount recognized $ (49,338 ) $ (32,229 ) $ (22,145 ) $ (26,063 ) Amounts recognized in accumulated other comprehensive income (loss) consist of: U.S. Foreign December 31, December 31, 2018 2017 2018 2017 Prior service cost $ — $ — $ (170 ) $ — Net gain (loss) 1,618 13,943 (2,133 ) (3,923 ) Gross amount recognized 1,618 13,943 (2,303 ) (3,923 ) Deferred income taxes (400 ) (3,444 ) 474 1,052 Net amount recognized $ 1,218 $ 10,499 $ (1,829 ) $ (2,871 ) Components of net periodic benefit cost consist of: U.S. Foreign Years ended Years ended 2018 2017 2016 2018 2017 2016 Service cost $ 1,019 $ 1,219 $ 2,130 $ 3,566 $ 3,686 $ 2,106 Interest cost 9,599 10,115 7,680 3,340 3,271 2,224 Expected return on plan assets (12,851 ) (12,277 ) (9,293 ) (3,311 ) (3,208 ) (2,038 ) Amortization of net (gain) loss — — — 49 (9 ) (10 ) Curtailment gain recognized (576 ) — (1,311 ) (340 ) — (517 ) Settlement (gain) loss recognized — (48 ) 152 (11 ) — — Net periodic expense (benefit) $ (2,809 ) $ (991 ) $ (642 ) $ 3,293 $ 3,740 $ 1,765 All components of net periodic benefit cost other than service cost are presented within other expense (income), net in the Company’s consolidated statements of operations. There is a nominal amount of estimated net actuarial gains and prior service costs for the Company’s defined benefit pension plans that will be amortized from accumulated other comprehensive income (loss) into net periodic benefit cost in 2019 . The total accumulated benefit obligation as of December 31, 2018 and 2017 for the Company’s U.S. pension plans was $244,580 and $257,882 , respectively. The total accumulated benefit obligation as of December 31, 2018 and 2017 for the Company’s foreign pension plans was $107,910 and $114,095 , respectively. The following table presents selected information about the Company’s pension plans with accumulated benefit obligations in excess of plan assets: U.S. Foreign December 31, December 31, 2018 2017 2018 2017 Projected benefit obligation $ 246,311 $ 261,102 $ 82,656 67,750 Accumulated benefit obligation 244,580 257,882 78,862 64,526 Fair value of plan assets 195,755 218,374 57,670 42,632 Significant weighted average assumptions used in determining the pension obligations include the following: U.S. Foreign December 31, December 31, 2018 2017 2018 2017 Discount rate 4.32 % 3.74 % 3.01 % 2.91 % Rate of compensation increase (1) 3.00 % 3.00 % 2.44 % 2.57 % Significant weighted average assumptions used in determining net periodic benefit cost include the following: U.S. Foreign Years ended Years ended 2018 2017 2016 2018 2017 2016 Discount rate 3.74 % 4.24 % 4.02 % 2.91 % 2.99 % 5.16 % Rate of compensation increase (1) 3.00 % 3.00 % 3.10 % 2.57 % 2.97 % 3.95 % Expected return on assets 6.00 % 6.37 % 6.34 % 3.52 % 3.58 % 5.62 % (1) Includes only plans not frozen to benefit accruals for the respective periods. The discount rate for each of the U.S. plans was determined by utilizing a yield curve model. The model develops a spot rate curve based on the yields available from a broad-based universe of high quality corporate bonds. The discount rate is then set as the weighted average spot rate, using the respective plan’s expected benefit cash flows as the weights. In determining the expected return on U.S. plan assets, the Company considers the relative weighting of plan assets, the historical performance of total plan assets and individual asset classes, and expected future performance. In addition, the Company may consult with and consider the opinions of our external advisors in developing appropriate return benchmarks. The investment objective for the U.S. plans is to generate returns sufficient to meet future obligations. The strategy to meet the objective includes generating attractive returns using higher returning assets such as equity securities and balancing risk using less volatile assets such as fixed income securities. The U.S. plans invest in an allocation of assets across the two broadly-defined financial asset categories of equity and fixed income securities. The target allocations for the plan assets across the three U.S. plans are as follows: 45% equity securities and 55% fixed income investments for the PQ Corporation Retirement Plan; 40% equity securities and 60% fixed income investments for the Eco Services Pension Equity Plan; and 45% equity securities and 55% fixed income investments for the Eco Services Hourly Pension Plan. Similar considerations are applied to the investment objectives of the non-U.S. plans as well as the asset classes available in each location and any legal restrictions on plan investments. The Company classifies plan assets based upon a fair value hierarchy (see Note 5 to these consolidated financial statements for further information). The classification of each asset within the hierarchy is based on the lowest level input that is significant to its measurement. The fair value hierarchy consists of three levels as follows: • Level 1—Values are unadjusted quoted prices for identical assets and liabilities in active markets accessible at the measurement date. Active markets provide pricing data for trades occurring at least weekly and include exchanges and dealer markets. Level 1 assets primarily include investments in publicly traded equity securities and mutual funds. These securities (or the underlying investments of the funds) are actively traded and valued using quoted prices for identical securities from the market exchanges. • Level 2—Inputs include quoted prices for similar assets or liabilities in active markets, quoted prices from those willing to trade in markets that are not active, or other inputs that are observable or can be corroborated by market data for the term of the instrument. Such inputs include market interest rates and volatilities, spreads and yield curves. Level 2 assets primarily consist of fixed-income securities and comingled funds that are not actively traded or whose underlying investments are valued using observable marketplace inputs. The fair value of plan assets invested in fixed-income securities is generally determined using valuation models that use observable inputs such as interest rates, bond yields, low-volume market quotes and quoted prices for similar assets. Plan assets that are invested in comingled funds are valued using a unit price or net asset value (“NAV”) that is based on the underlying investments of the fund. • Level 3—Certain inputs are unobservable (supported by little or no market activity) and significant to the fair value measurement. Unobservable inputs reflect the Company’s best estimate of what hypothetical market participants would use to determine a transaction price for the asset or liability at the reporting date. Level 3 assets include investments covered by insurance contracts and real estate funds valued using significant unobservable inputs. The following tables set forth by level, within the fair value hierarchy, plan assets at fair value: December 31, 2018 Total Level 1 Level 2 Level 3 Cash and cash equivalents (1) $ 57,000 $ 56,925 $ 75 $ — Equity securities: U.S. investment funds 35,103 35,103 — — International investment funds 44,508 24,040 20,468 — Fixed income securities: Government securities 10,121 — 10,121 — Corporate bonds 77,229 72,216 5,013 — Investment fund bonds 25,152 7,665 17,487 — Other: Insurance contracts 38,429 — 33,408 5,021 Total $ 287,542 $ 195,949 $ 86,572 $ 5,021 December 31, 2017 Total Level 1 Level 2 Level 3 Cash and cash equivalents $ 1,072 $ 934 $ 138 $ — Equity securities: U.S. investment funds 56,309 43,625 12,684 — International investment funds 70,308 28,827 41,481 — Fixed income securities: Government securities 11,433 — 11,433 — Corporate bonds 82,585 77,685 4,900 — Investment fund bonds 54,263 7,719 46,544 — Other: Insurance contracts 38,922 — 34,772 4,150 Total $ 314,892 $ 158,790 $ 151,952 $ 4,150 (1) Level 1 balance includes $55,905 of cash and cash equivalents held by two of the Company’s U.S. defined benefit pension plans. The investments in equity securities and fixed income securities previously held by these plans were liquidated into cash and cash equivalents in December 2018 in preparation for a transfer of plan assets to a new custodian. This transfer was completed in January 2019. The changes in the Level 3 pension plan assets are as follows for the years ended December 31: Insurance Contracts 2018 2017 Beginning balance $ 4,150 $ 3,286 Actual return on plan assets 10 (41 ) Benefits paid (385 ) (48 ) Contributions 461 466 Exchange rate changes and other 785 487 Ending balance $ 5,021 $ 4,150 The Company expects to contribute $972 to the U.S. pension plans and $4,334 to the foreign pension plans in 2019 . The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid: Year U.S. Foreign 2019 $ 15,369 $ 3,115 2020 16,253 2,769 2021 16,966 2,952 2022 15,894 3,366 2023 15,823 3,630 Years 2024-2028 78,304 23,111 Certain of the Company’s foreign subsidiaries maintain other defined benefit plans that are consistent with statutory practices. These plans are not included in the disclosures above as they are not significant to the Company’s consolidated financial statements. Supplemental Retirement Plans The following tables summarize changes in the benefit obligation, plan assets and funded status of the Company’s defined benefit supplementary retirement plans, as well as the components of net periodic benefit cost, including key assumptions: December 31, 2018 2017 Change in benefit obligation: Benefit obligation at beginning of period $ 12,781 $ 13,225 Interest cost 450 489 Benefits paid (1,070 ) (1,179 ) Actuarial (gains) losses (293 ) 246 Benefit obligation at end of period $ 11,868 $ 12,781 Change in plan assets: Fair value of plan assets at beginning of period $ — $ — Employer contributions 1,070 1,179 Benefits paid (1,070 ) (1,179 ) Fair value of plan assets at end of period $ — $ — Funded status of the plans (underfunded) $ (11,868 ) $ (12,781 ) Amounts recognized in the consolidated balance sheets consist of: December 31, 2018 2017 Current liability $ (1,105 ) $ (1,115 ) Noncurrent liability (10,763 ) (11,667 ) Accumulated other comprehensive income 795 573 Net amount recognized $ (11,073 ) $ (12,209 ) Amounts recognized in accumulated other comprehensive income consist of: December 31, 2018 2017 Net gain $ 1,055 $ 761 Gross amount recognized 1,055 761 Deferred income taxes (260 ) (188 ) Net amount recognized $ 795 $ 573 Components of net periodic benefit cost consist of: Years ended 2018 2017 2016 Interest cost $ 450 $ 489 $ 328 Net periodic expense $ 450 $ 489 $ 328 Interest cost is presented within other expense (income), net in the Company’s consolidated statements of operations. There are no estimated net actuarial gains for the Company’s defined benefit supplementary retirement plans that will be amortized from accumulated other comprehensive income into net periodic benefit cost in 2019 . The accumulated benefit obligation of the Company’s defined benefit supplemental retirement plans as of December 31, 2018 and 2017 was $11,868 and $12,781 , respectively. The discount rate used in determining the defined benefit supplemental retirement plan obligation was 4.20% and 3.60% as of December 31, 2018 and 2017 , respectively. The discount rate used in determining net periodic benefit cost was 3.60% , 3.90% and 3.40% for the years ended December 31, 2018 , 2017 and 2016 , respectively. There was no rate of compensation increase for any of the periods presented, as all future accruals were frozen for the defined benefit supplementary retirement plans as of December 31, 2006. The Company expects to contribute $1,105 to the defined benefit supplementary retirement plans in 2019 . The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid: Year Amount 2019 $ 1,105 2020 1,076 2021 1,045 2022 1,009 2023 970 Years 2024-2028 4,276 Other Postretirement Benefit Plans The following tables summarize changes in the benefit obligation, plan assets and funded status of the Company’s other postretirement benefit plans as well as the components of net periodic benefit cost, including key assumptions: December 31, 2018 2017 Change in benefit obligation: Benefit obligation at beginning of period $ 4,612 $ 4,620 Service cost 16 21 Interest cost 150 174 Employee contributions 251 251 Plan amendments (271 ) — Benefits paid (1,061 ) (923 ) Medical subsidies received 74 — Premiums paid (66 ) (3 ) Actuarial (gains) losses 172 418 Translation adjustment (63 ) 54 Benefit obligation at end of period $ 3,814 $ 4,612 Change in plan assets: Fair value of plan assets at beginning of period — — Employer contributions 802 675 Employee contributions 251 251 Benefits paid (1,061 ) (923 ) Medical subsidies received 74 — Premiums paid (66 ) (3 ) Fair value of plan assets at end of period $ — $ — Funded status of the plans (underfunded) $ (3,814 ) $ (4,612 ) Amounts recognized in the consolidated balance sheets consist of: December 31, 2018 2017 Current liability $ (581 ) $ (561 ) Noncurrent liability (3,233 ) (4,051 ) Accumulated other comprehensive income 830 885 Net amount recognized $ (2,984 ) $ (3,727 ) Amounts recognized in accumulated other comprehensive income consist of: December 31, 2018 2017 Prior service credit $ 525 $ 366 Net gain 500 719 Gross amount recognized 1,025 1,085 Deferred income taxes (195 ) (200 ) Net amount recognized $ 830 $ 885 Components of net periodic benefit cost consist of: Years ended 2018 2017 2016 Service cost $ 16 $ 21 $ 37 Interest cost 150 174 151 Amortization of prior service credit (112 ) (78 ) — Amortization of net gain (26 ) (45 ) (17 ) Net periodic expense $ 28 $ 72 $ 171 All components of net periodic benefit cost other than service cost are presented within other expense (income), net in the Company’s consolidated statements of operations. The estimated prior service credit for the Company’s retiree health plans that will be amortized from accumulated other comprehensive income into net periodic benefit cost in 2019 is $130 . The estimated net actuarial gain for the Company’s retiree health plans that will be amortized from accumulated other comprehensive income into net periodic benefit cost in 2019 is $32 . The discount rate used in determining the other postretirement benefit plan obligation was 3.53% and 3.74% as of December 31, 2018 and 2017 , respectively. The discount rate used in determining net periodic benefit cost was 3.53% , 3.74% and 3.92% for the years ended December 31, 2018 , 2017 and 2016 , respectively. Assumed health care cost trend rates were as follows: December 31, 2018 2017 Immediate trend rate 6.59% 6.84% Ultimate trend rate 4.50% 4.50% Year that the rate reaches ultimate trend rate 2035 2035 A 1% change in the assumed health care cost trend would have increased (decreased) the accumulated postretirement benefit obligation as of December 31, 2018 and the periodic postretirement benefit cost for the year then ended as follows: 1% Increase 1% Decrease Accumulated postretirement benefit obligation $ 157 $ (138 ) Periodic postretirement benefit cost 6 (5 ) The Company expects to contribute $581 to the retiree health plans in 2019 . The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid: Year Amount 2019 $ 581 2020 514 2021 388 2022 313 2023 272 Years 2024-2028 915 There are no expected Medicare subsidy receipts expected in future periods. Certain of the Company’s foreign subsidiaries maintain other postretirement benefit plans that are consistent with statutory practices. These plans are not included in the disclosures above as they are not significant to the Company’s consolidated financial statements. Defined Contribution Plans The Company also has defined contribution plans covering domestic employees of the Company and certain subsidiaries. The Company recorded expenses of $12,585 , $13,103 and $6,864 related to these plans for the years ended December 31, 2018 , 2017 and 2016 , respectively.

Earnings per Share

Earnings per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings per Share	21. Earnings per Share: During the period January 1, 2016 to May 4, 2016, the date of the Business Combination, the Company was structured as a single member LLC, with capital contributions from affiliates of CCMP, the Company’s board of managers and management represented by a class of membership units (“Eco Services Class A Units” or “Eco Services membership units”). During this period, Eco Services also granted incentive awards to certain employees, directors and affiliates in the form of Class B Units of Eco Services (the “Eco Services Class B Units”), which provided recipients with the option to purchase Eco Services Class A Units upon the attainment of certain vesting and other restrictions (see Note 22 to these consolidated financial statements for further information regarding the Company’s equity incentive plans). At the date of the Business Combination, the existing Eco Services Class A Units and legacy PQ Holdings equity were converted to common stock of PQ Group Holdings. None of the Eco Class B Units had been exercised prior to the Business Combination, and all Eco Class B Units converted to common stock options of PQ Group Holdings at the date of the Business Combination (see Note 22 ). Basic earnings per share is calculated as income (loss) available to common stockholders, divided by the weighted average number of common shares outstanding during the period. The weighted average number of common shares outstanding during the period for the computation of basic earnings per share excludes restricted stock awards that have legally been issued but are nonvested during the period, as the sale of these shares is prohibited pending satisfaction of certain vesting conditions by the award recipients in order to earn the rights to the shares (see Note 22 to these consolidated financial statements for further information regarding outstanding nonvested restricted stock awards). Diluted earnings per share is calculated as income (loss) available to common stockholders, divided by the weighted average number of common and potential common shares outstanding during the period for each class of common stock, if dilutive. Potential shares reflect unvested restricted stock awards and restricted stock units with service conditions as well as options to purchase common stock, which have been included in the diluted earnings per share calculation using the treasury stock method. For both the basic and dilutive weighted average shares calculations, as a result of the Business Combination, the number of Eco Services membership units outstanding from January 1, 2016 through May 4, 2016, the date of the Business Combination, were computed on the basis of the weighted average units outstanding for Eco Services during the respective periods multiplied by the exchange ratio established for common stock as part of the Business Combination. The reconciliation from basic to diluted weighted average shares outstanding is as follows: Years ended 2018 2017 2016 Weighted average shares outstanding – Basic 133,380,567 111,299,670 78,016,005 Dilutive effect of unvested common shares and restricted stock units with service conditions and assumed stock option exercises and conversions 1,304,364 369,367 — Weighted average shares outstanding – Diluted 134,684,931 111,669,037 78,016,005 Basic and diluted earnings per share are calculated as follows: Years ended 2018 2017 2016 Numerator: Net income (loss) attributable to PQ Group Holdings Inc. $ 58,300 $ 57,603 $ (79,746 ) Denominator: Weighted average shares outstanding – Basic 133,380,567 111,299,670 78,016,005 Weighted average shares outstanding – Diluted 134,684,931 111,669,037 78,016,005 Net income (loss) per share: Basic income (loss) per share $ 0.44 $ 0.52 $ (1.02 ) Diluted income (loss) per share $ 0.43 $ 0.52 $ (1.02 ) The table below presents the details of the Company’s equity-based awards outstanding at the end of each respective year that were excluded from the calculation of diluted earnings per share: December 31, 2018 2017 2016 Restricted stock awards with performance only targets not yet achieved 1,643,760 1,769,447 1,731,522 Stock options with performance only targets not yet achieved 586,253 586,523 417,086 Anti-dilutive restricted stock awards and restricted stock units 10,296 — 751,410 Anti-dilutive stock options 863,063 621,747 1,381,352 Restricted stock awards and stock options with performance only vesting conditions are not included in the dilution calculation, as the performance targets have not been achieved as of the end of the respective years. Anti-dilutive awards are not included in the dilution calculation, as their inclusion would have the effect of increasing diluted income per share.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	22. Stock-Based Compensation: Eco Services Class B Units Prior to the Business Combination, the Company recognized stock-based compensation expense for incentive awards issued under the Eco Services Group Holdings Incentive Unit Agreement dated December 29, 2014 (the “Incentive Unit Agreement”). Under the Incentive Unit Agreement, the Company granted Eco Services Class B Units to certain employees, directors and affiliates of the Company. As of December 31, 2015 and immediately prior to the date of the Business Combination on May 4, 2016, there were 25,093 of Eco Services Class B Units outstanding with an exercise price of $1,000 /unit. Of this total, 10,674 Eco Services Class B Units granted to employees (the “Management Awards”) had two vesting criteria, in which 50% were subject to a service (time-based) vesting condition and 50% were subject to a performance condition based upon the occurrence of specific liquidity events. The Eco Services Class B Units subject to the service condition vested 25% annually, with the first annual vesting date of December 1, 2015. The remaining 14,419 of Eco Services Class B Units awarded to directors and affiliates (the “Director Awards”) were subject to a service vesting condition only, consistent with that of the Management Awards. The Eco Services Class B Units did not have a contractually defined maximum term. PQ Group Holdings Awards In conjunction with the Business Combination, the Company adopted an equity incentive plan, namely the PQ Group Holdings Inc. Stock Incentive Plan (“2016 Plan”). Under the terms of the 2016 Plan, the Company is authorized to issue a total of 8,017,038 shares for common stock awards to employees, directors and affiliates of the Company. Immediately preceding the IPO as of September 30, 2017, awards with respect to 7,644,518 shares of common stock had been issued under the 2016 Plan. In connection with the IPO, the Company’s board of directors adopted the PQ Group Holdings Inc. 2017 Omnibus Incentive Plan (the “2017 Plan”). Subsequent to the IPO, all equity incentive awards are granted under the 2017 Plan. The number of shares of common stock reserved for issuance under the 2017 Plan is 7,344,000 shares, which amount is increased by the 372,520 shares remaining available for grant under the 2016 Plan as of the 2017 Plan adoption. Shares that become available for issuance pursuant to the 2016 Plan as a result of forfeiture, cancellation or termination for no consideration will be available for future awards under the 2017 Plan. Shares underlying awards granted under the 2017 Plan that are forfeited, canceled, terminated for no consideration, settled in cash or are withheld for exercise, taxes, etc. will not be deemed as delivered and will also be available for future issuance under the 2017 Plan. At December 31, 2018 , 5,396,119 shares of common stock were available for issuance under the 2017 Plan. Stock Options As part of the Business Combination, the 25,093 of outstanding Eco Services Class B Units at the date of the Business Combination were canceled and replaced with 1,378,302 of options to purchase PQ Group Holdings common stock at an exercise price of $8.04 /share. The Eco Services Class B Units were replaced by common stock options in accordance with a formula to convert such awards, plus a vested cash component. The terms of the new awards were substantially identical to those in effect prior to the Business Combination, except for adjustments to the underlying number of shares (based on the conversion ratio) and the exercise price, which was based on PQ Group Holdings common stock. Additionally, although the Eco Services Class B Units did not have a contractually defined maximum term, the maximum term of the common stock options is ten years . The Company accounted for the cancellation and replacement (including a cash component) as a combination of a modification and a cash settlement. This resulted in no incremental compensation cost recognized at the time of the modification, but led to an acceleration of $1,174 of previously measured but unrecognized compensation cost. In addition to the Eco Services Class B Units that were canceled and replaced at the time of the Business Combination, the Company exchanged the outstanding option awards of PQ Holdings for options of PQ Group Holdings in connection with the merger. The terms of the PQ Group Holdings awards were substantially identical to those of the PQ Holdings awards, including the number of underlying shares and vesting conditions, with the exception of an exercise price of $8.04 /share for the common stock options. There are various vesting conditions associated with the exchanged awards, including satisfaction of certain service and performance based conditions. Beginning with the date of the Business Combination of May 4, 2016 through the Company’s IPO, the Company granted common stock options with either service or performance vesting conditions, all with a maximum contractual term of ten years . Starting on October 2, 2017 in connection with the Company’s IPO and subsequent to this date, the Company’s stock option grants have been subject to graded vesting conditions based on service and a maximum contractual term of ten years . The following table summarizes the activity of common stock options for the period from the date of the Business Combination of May 4, 2016 through the year ended December 31, 2018 , which includes both the Eco Services Class B Units that were canceled and replaced, as well as the PQ Holdings options that were exchanged as part of the Business Combination: Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Granted/assumed on May 4, 2016 in connection with the Business Combination 1,738,527 $ 7.80 Granted 538,908 $ 8.05 Forfeited (478,997 ) $ 7.49 Outstanding at December 31, 2016 1,798,438 $ 7.96 Granted 1,051,496 $ 13.70 Exercised (32,366 ) $ 8.04 Forfeited (102,398 ) $ 7.98 Outstanding at December 31, 2017 2,715,170 $ 10.18 Granted 241,316 $ 17.50 Exercised (15,332 ) $ 8.51 Outstanding at December 31, 2018 2,941,154 $ 10.79 7.71 $ 14,452 Exercisable at December 31, 2018 1,629,969 $ 10.19 7.71 $ 8,748 The aggregate intrinsic value per the above table represents the difference between the fair value the Company’s common stock on the last trading day of the reporting period (determined in accordance with the plan terms) and the exercise price of in-the-money stock options multiplied by the respective number of stock options as of that date. The total intrinsic value of stock options exercised during the years ended December 31, 2018 and 2017 and the resulting tax benefits recognized by the Company were not material for either year. Additionally, cash proceeds received by the Company during the year ended December 31, 2018 were not material. The Company did not receive any cash proceeds from the exercise of stock options during the year ended December 31, 2017, as the Company withheld shares in satisfaction of the exercise price and taxes due. The fair values of PQ Group Holdings common stock options granted during the years ended December 31, 2018 , 2017 and 2016 were determined on the respective grant dates using a Black-Scholes option pricing model with the following weighted-average assumptions: 2018 2017 2016 Expected term (in years) 5.75 5.85 5.00 Expected volatility 26.38 % 34.85 % 45.79 % Risk-free interest rate 2.86 % 2.00 % 1.54 % Expected dividend yield 0.00 % 0.00 % 0.00 % Weighted average grant date fair value of options granted $ 5.47 $ 4.71 $ 3.33 With the limited experience of the Company with respect to historical exercise and forfeiture rates or patterns, the expected term for stock option grants in 2016 was estimated in the context of the service award vesting period as well as the timeframe for a liquidity event for the performance awards, along with the ten-year contractual maximum term, while the Company was still privately held. Beginning in 2017, the Company used the simplified method for plain vanilla stock options to estimate the expected term assumption, since the Company lacks sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term due to the limited period of time its common stock has been publicly traded. The application of the simplified method involves calculating the average of the time-to-vesting period and the total contractual life of the options. The Company applied a consistent methodology for the remainder of the assumptions in the Black-Scholes option pricing model for stock option grants during the years ended December 31, 2018 , 2017 and 2016 . The expected volatility was compared to a range of the actual stock price volatility of a peer group of companies. The risk-free interest rate was based on U.S. Treasury rates in effect at the time of the grant commensurate with the expected term. There was no dividend yield assumption since the Company has not paid dividends nor does it have an expectation of future dividend payouts. Restricted Stock Awards and Restricted Stock Units In addition to the exchange of the PQ Holdings options at the date of the Business Combination on May 4, 2016, the Company also exchanged unvested PQ Holdings restricted stock awards for 2,444,070 shares of restricted stock awards of PQ Group Holdings. The restricted stock awards were issued at substantially identical terms to the original PQ Holdings awards, with the exception of a new price ascribed to the shares. The restricted stock awards were subject to the same vesting requirements as the original awards, which included awards with vesting conditions based on (1) service only, (2) performance only, or (3) a combination of service and performance conditions, dependent on which event occurs first. The vesting requirements for the majority of these awards were based upon the achievement of a performance condition. As defined in the award agreements, each award subject to the performance condition fully vests upon the occurrence of a defined liquidity event upon which certain investment funds affiliated with CCMP receive proceeds exceeding certain thresholds. Although achievement of the performance condition is subject to continued service with the Company, the terms of awards issued with performance conditions stipulate that the performance vesting condition can be attained for a period of six months following separation from service. The same performance vesting condition for the Company’s restricted stock awards also governs the achievement of the performance vesting condition for the Company’s stock options. With the exception of 14,498 and 21,067 of restricted stock awards granted on December 27, 2018 and October 2, 2017, respectively, both of which immediately vested and were valued based on the average of the high and low trading prices of the Company’s common stock on the NYSE on the preceding trading day, based on the Company’s policy for valuing such awards, all of the Company’s restricted stock awards were granted prior to the IPO. As a result, the Company valued the pre-IPO restricted stock awards at grant using multiples of EBITDA and the income approach, based on a discounted free cash flow model. In addition to restricted stock awards, the Company has granted restricted stock units as part of its equity incentive compensation program. The value of the restricted stock unit grants were based on the average of the high and low trading prices of the Company’s common stock on the NYSE on the preceding trading day, based on the Company’s policy for valuing such awards, and have graded vesting conditions based on service. The following table summarizes the activity of restricted stock awards and restricted stock units for the period from the date of the Business Combination of May 4, 2016 through the year ended December 31, 2018 , which includes the PQ Holdings restricted stock awards that were exchanged as part of the Business Combination: Restricted Stock Awards Restricted Stock Units Number of Weighted Average Grant Date Fair Value (per share) Number of Weighted Average Grant Date Fair Value (per share) Granted/assumed on May 4, 2016 in connection with the Business Combination 2,444,070 $ 9.27 — $ — Granted 266,955 $ 12.32 — $ — Vested (207,915 ) $ 12.32 — $ — Forfeited (20,178 ) $ 10.52 — $ — Nonvested as of December 31, 2016 2,482,932 $ 9.34 — $ — Granted 51,907 $ 16.11 1,654,690 $ 16.97 Vested (187,837 ) $ 12.84 — $ — Forfeited (250,365 ) $ 12.03 — $ — Nonvested as of December 31, 2017 2,096,637 $ 8.87 1,654,690 $ 16.97 Granted 14,498 $ 13.80 161,598 $ 16.12 Vested (223,298 ) $ 12.18 (797,859 ) $ 16.97 Forfeited (117,177 ) $ 8.04 (19,643 ) $ 16.97 Nonvested as of December 31, 2018 1,770,660 $ 8.39 998,786 $ 16.83 Business Combination and Equity Restructuring The exchange of the PQ Holdings stock options and restricted stock awards for similar awards of PQ Group Holdings in the context of the Business Combination was accounted for as a modification of the awards. As a result, the cost of the replacement awards of PQ Group Holdings represented a combination of both pre- and post-merger services. The amount attributable to services prior to the Business Combination in connection with the modification was $1,400 , and is considered part of the consideration transferred in the Business Combination (see Note 7 to these consolidated financial statements for further information). The remainder of the cost is attributed to post-merger services and is being recognized over the respective remaining vesting periods. The Company’s equity restructuring which occurred prior the IPO (see Note 1 to these consolidated financial statements for further information) also constituted an event subject to modification accounting for stock-based compensation awards. However, the change to the equity incentive awards of the Company was designed to preserve the fair value of the awards before and after the reclassification and stock split (based on the existing antidilution provisions of the 2016 Plan), and included the same terms and were classified in the same manner as the equity awards preceding the modification. As a result, no incremental compensation cost was recognized by the Company. Total Stock-Based Compensation Expense For the years ended December 31, 2018 , 2017 and 2016 , total stock-based compensation expense for the Company (inclusive of both the Eco Services Class B Units prior to the Business Combination and the awards replaced or exchanged at the consummation of the Business Combination) was $19,464 , $8,799 and $7,029 , respectively. The income tax benefit recognized in the statements of operations for the years ended December 31, 2018 , 2017 and 2016 was $4,809 , $3,345 and $2,660 . As of December 31, 2018 , there was $2,484,141 of total unrecognized compensation cost related to nonvested stock options subject to service vesting conditions. As of December 31, 2018 , there was $342,724 of total unrecognized compensation cost related to nonvested restricted stock awards subject to service vesting conditions. As of December 31, 2018 , there was $13,945,550 of total unrecognized compensation cost related to nonvested restricted stock units. No expense has been recognized for any stock-based compensation awards subject to the performance condition for the years ended December 31, 2018 , 2017 and 2016 , as the performance-based criteria was not achieved nor considered probable of achievement. Awards issued with performance conditions vest based on the occurrence of a defined liquidity event upon which certain investment funds affiliated with CCMP receive proceeds exceeding certain thresholds. All of the Company’s equity incentive awards with performance-based vesting, whether in the form of stock options or restricted stock awards, are subject to achievement of the same performance condition. If an exit event occurs that exceeds the defined threshold, then all performance-based awards of the Company vest 100% , with no potential for partial vesting or excess achievement. If an exit event or events occur with no further possibility of meeting the defined threshold, then all of the Company’s awards subject to the performance vesting condition will be forfeited. In addition to the defined liquidity event, subsequent to the Company’s IPO, the performance vesting condition can also be achieved if the average closing trading price of the Company’s common stock on the NYSE over any consecutive ten-day trading period equals or exceeds a price that would be equivalent to the achievement of the threshold proceeds to CCMP. See Note 21 to these consolidated financial statements for further information on the number of awards outstanding subject to performance-based vesting.

Commitments and Contingent Liab

Commitments and Contingent Liabilities	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities	23. Commitments and Contingent Liabilities: Environmental Contingencies There is a risk of environmental impact in chemical manufacturing operations. The Company’s environmental policies and practices are designed to comply with existing laws and regulations and to minimize the possibility of significant environmental impact. The Company is also subject to various other lawsuits and claims with respect to matters such as governmental regulations, labor and other actions arising out of the normal course of business. While management believes that the liabilities resulting from such lawsuits and claims are not probable or reasonably estimable, certain accruals have been reflected in the Company’s consolidated financial statements, some of which are described in detail within this note. The Company has recorded a reserve of $ 873 and $ 1,245 as of December 31, 2018 and 2017 , respectively, to address remaining subsurface remedial and wetlands/marsh management activities at the Company’s Martinez, CA site. Although currently a sulfuric acid regeneration plant, the site originally was operated by Mountain Copper Company (“Mococo”) as a copper smelter. Also, the site sold iron pyrite to various customers and allowed their customers to deposit waste iron pyrite cinder and slag on the site. The property is adjacent to Peyton Slough, where Mococo had a permitted discharge point from its process. In 1997, the San Francisco Bay Regional Water Quality Control Board (“RWQCB”) required characterization and remediation of Peyton Slough for Copper, Zinc and Acidic Soils. Various remediation activities were undertaken and completed, and the site has received final concurrence from the Army Corps with respect to the completed work. The RWQCB has agreed that Eco Services has achieved the goals for vegetative cover, but the current marsh condition is not sustainable without continued operation of the tide gates. The Company is continuing to work with the RWQCB on a plan to involve the County and work towards development of an alliance for operating, maintaining and funding the tide gates in the future. As of December 31, 2018 and 2017 , the Company has recorded a reserve of $ 984 and $ 1,220 , respectively, for subsurface remediation and the Soil Vapor Extraction Project at the Company’s Dominguez, CA site. In the 1980s and 1990s, the EPA and the Los Angeles Regional Water Quality Control Board conducted investigations of the site due to historic chlorinated pesticide and chlorinated solvent use. Soil and groundwater beneath the site were impacted by chlorinated solvents and associated breakdown products, petroleum hydrocarbons, chlorinated pesticides and metals. A Corrective Measures Plan approved in October 2011 requires (1) soil vapor extraction (“SVE”) in affected areas, (2) covering of unpaved areas containing pesticide impacted soil, and (3) annual groundwater monitoring of the perched water-bearing zone. Installation of the SVE unit has been completed and startup has occurred. The California Department of Toxic Substances Control (“DTSC”) has granted conditional approval of the Company’s soil management, and monitoring and maintenance plans. Most recently, the DTSC is requiring the Company to delineate the PCE plume on the eastern boundary of the site. The Company has submitted an action plan to address this matter and is awaiting comments from the DTSC. Leases The Company has entered into various lease agreements for the rental of office and plant facilities, railcars, machinery and equipment, substantially all of which are classified as operating leases. Total rent expense under these agreements was $25,082 , $22,704 and $16,315 for the years ended December 31, 2018 , 2017 and 2016 , respectively. Total rent due under non-cancelable operating lease commitments as of December 31, 2018 is: Year Amount 2019 $ 18,457 2020 14,344 2021 11,432 2022 8,354 2023 6,198 Thereafter 17,477 $ 76,262 Purchase Commitments The Company has entered into short and long-term purchase commitments for various key raw materials and energy requirements. The purchase obligations include agreements to purchase goods that are enforceable and legally binding, and that specify all significant terms. The purchase commitments covered by these agreements are with various suppliers and total approximately $56,642 as of December 31, 2018 . Purchases under these agreements are expected to be as follows: Year Amount 2019 $ 28,485 2020 19,820 2021 2,039 2022 1,450 2023 1,305 Thereafter 3,543 $ 56,642 Letters of Credit At December 31, 2018 , the Company had outstanding letters of credit of $19,796 . Letters of credit are guarantees of payment to third parties. The Company’s letters of credit are used primarily as collateral for various items, including environmental, energy and insurance payments. The letters of credit are supported by the Company’s ABL facility.

Restructuring and Other Related

Restructuring and Other Related Costs	12 Months Ended
	Dec. 31, 2018
Restructuring and Related Activities [Abstract]
Restructuring and Other Related Costs	24. Restructuring and Other Related Costs: The following table presents the components of restructuring and other related costs for the years ended December 31, 2018 , 2017 and 2016 included in other operating expense, net, in the accompanying consolidated statements of operations: Years ended 2018 2017 2016 Severance and other employee costs related to Eco Services restructuring plan $ — $ 830 $ 5,093 Severance and other employee costs related to performance materials plant closure 885 4,711 — Other related costs 5,323 2,949 7,537 $ 6,208 $ 8,490 $ 12,630 Eco Services Restructuring Plan On July 30, 2014, Eco Services, a newly formed Delaware limited liability company and indirect subsidiary of certain investment funds affiliated with CCMP, entered into an Asset Purchase Agreement with Solvay USA, Inc. (“Solvay”), a Delaware corporation, which provided for the sale, transfer and assignment by Solvay and the acquisition, acceptance and assumption by Eco Services, of substantially all of the assets of Solvay’s Eco Services business unit of Solvay’s regeneration and virgin sulfuric acid production business operations in the United States (the “2014 Acquisition”). Prior to the Asset Purchase Agreement with Solvay, Eco Services operated as a business unit within Solvay, which is an indirect, wholly owned subsidiary of Solvay SA. Subsequent to the 2014 Acquisition, the Company initiated a restructuring plan designed to improve organizational efficiency and streamline the operations of Eco Services as a stand-alone company. The primary impact of the plan to the Company’s consolidated results of operations was the recognition of severance costs related to a reduction-in-force. These costs included benefits payable under ongoing Company severance plan arrangements, whereby payments are attributable to employee services rendered with benefits that accumulate over time. The liabilities and associated charges related to these severance costs are recognized by the Company when payment of the benefits becomes probable and estimable. The restructuring plan was substantially complete in early 2017. Costs related to the restructuring plan affected employees in the Company’s EC&S segment, although these costs are excluded from the segment’s measure of profitability of Adjusted EBITDA (see Note 13 to these consolidated financial statements for further information). Performance Materials Plant Closure In September 2017, the Company approved and announced a plan to consolidate its manufacturing operations in Europe for the performance materials product group and close its facility in Kirchheimbolanden, Germany, and subsequently reduced production. The plan was part of the Company’s overall strategy with respect to the Acquisition (see Note 8 to these consolidated financial statements) and the realization of cost and other synergies in connection with the transaction. As a result of a change in the market and increased customer demand for the products produced at this facility, the Company intends to keep the facility open and expanded production at this facility during the third quarter of 2018 from the previously reduced levels. However, the Company continues to pay its obligations to the individuals originally separated from service as part of the reorganization, with additional payments anticipated through 2019, primarily for individuals who extended their separation dates as a result of the decision to continue operations at the facility. Costs related to the restructuring plan affected employees in the Company’s PM&C segment, although these costs are excluded from the segment’s measure of profitability of Adjusted EBITDA (see Note 13 to these consolidated financial statements for further information). The Company considers the restructuring plan related to the original decision to close the facility substantially complete, with no additional restructuring charges anticipated. Rollforward of Restructuring Liabilities The activity in the accrued liability balance associated with the Company’s restructuring plans, all of which related to severance and other employee costs, was as follows for the years ended December 31, 2018 , 2017 and 2016 : Eco Services Restructuring Plan Performance Materials Plant Closure Total Restructuring Charges Balance at December 31, 2015 $ 1,293 $ — $ 1,293 Restructuring charges 5,093 — 5,093 Cash payments (4,743 ) — (4,743 ) Balance at December 31, 2016 $ 1,643 $ — $ 1,643 Restructuring charges 830 4,711 5,541 Cash payments (2,258 ) (1,588 ) (3,846 ) Balance at December 31, 2017 $ 215 $ 3,123 $ 3,338 Restructuring charges — 581 581 Other adjustments — 304 304 Cash payments (215 ) (2,738 ) (2,953 ) Balance at December 31, 2018 $ — $ 1,270 $ 1,270 Other Related Costs The Company incurred severance and other costs of $5,323 , $2,949 and $7,537 for the years ended December 31, 2018 , 2017 and 2016 , respectively. These costs were not associated with formal restructuring plans and primarily related to severance charges for certain executives and employees, transition/duplicate staffing, professional fees and other expenses related to the Company’s organizational changes.

Long-term Supply Contract

Long-term Supply Contract	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Long-term Supply Contract	25. Long-term Supply Contract: As part of Solvay’s 2004 sale of its Specialty Phosphates business, Solvay agreed to continue to supply sulfuric acid to a customer in support of the phosphoric acid production for its specialty phosphates business under a preexisting supply agreement. This non-cancelable agreement extends to 2031, and was assumed by the Company in connection with the 2014 Acquisition. The liability associated with this unfavorable supply agreement was recorded at a fair value of $27,300 in connection with the 2014 Acquisition. The fair value was determined using the income method based on the differential of the estimated margin over the cost of the sulfuric acid per the market as compared to the below market margin included in the supply agreement, and the application of this excess differential to the anticipated volumes over the term of the agreement using a commensurate discount rate. In December 2018 , the customer to the supply agreement ceased production and closed the facility which utilized the Company’s sulfuric acid under the agreement. As such, all orders for sulfuric acid under the agreement were discontinued in December 2018 . Although the agreement is not cancelable, the likelihood is remote that the Company will be further obligated to supply the customer under the agreement since this is the only facility subject to the agreement, and there are no transfer or substitution rights under the agreement to another facility. As a result, the Company wrote-off the remaining supply contract liability of $20,612 at December 31, 2018 and recorded a corresponding gain to other operating expense, net as of December 31, 2018 . The liability was $22,250 at December 31, 2017 .

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	26. Related Party Transactions: The Company maintains certain policies and procedures for the review, approval and ratification of related party transactions to ensure that all transactions with selected parties are fair, reasonable and in the Company’s best interests. All significant relationships and transactions are separately identified by management if they meet the definition of a related party or a related party transaction. Related party transactions include transactions that occurred during the year, or are currently proposed, in which the Company was or will be a participant, and for which any related person had or will have a direct or indirect material interest. All related party transactions are reviewed, approved and documented by the appropriate level of the Company’s management in accordance with these policies and procedures. On December 29, 2014, PQ Holdings, CCMP and PQ Corporation entered into a consulting agreement relating to the provision of certain financial and strategic advisory services and consulting services. Similarly, the consulting agreement between PQ Holdings, INEOS Capital Partners and PQ Corporation was amended and restated. Under the new consulting agreements, the Company agreed to pay an annual management fee of $5,000 distributed to CCMP and INEOS AG equal to the Pro Rata Percentage, as defined, between CCMP and INEOS AG. These consulting agreements were terminated upon completion of the Company’s IPO on October 3, 2017. The Company recorded $3,777 and $3,584 of management advisory fees in other operating expense, net in the consolidated statements of operations for the years ended December 31, 2017 and 2016 , respectively. Transactions with Board of Directors In connection with the offering by PQ Corporation of $525,000 aggregate principal amount of Senior Unsecured Notes due 2022 in May 2016, a member of the Company’s board of directors purchased $4,000 in principal amount of such notes. Interest accrued on the notes at an annual rate equal to three-month LIBOR plus 10.75% , with a 1.0% LIBOR floor, payable and reset quarterly. The director received interest payments in respect of the notes totaling $362 and $300 during the years ended December 31, 2017 and 2016, respectively. The notes were partially redeemed in October 2017 in connection with the Company’s IPO, and redeemed in full in December 2017 in connection with the Company’s issuance and sale of the $300,000 Senior Unsecured Notes due 2025 (see Note 16 ). The director received $4,000 of principal amount of such notes as well as $338 related to the prepayment penalties in connection with these two transactions. Joint Venture Agreement The Company entered into a joint venture agreement (the “ZI Partnership Agreement”) in 1988 with CRI Zeolites Inc., a Royal Dutch Shell plc affiliate, to form Zeolyst International, our 50/50 joint venture partnership (the “Partnership”). Under the terms of the ZI Partnership Agreement, the Partnership leases certain land used in its Kansas City production facilities from PQ Corporation. This lease, which has been recorded as an operating lease, provided for rental payments of $295 , $295 and $187 during the years ended December 31, 2018 , 2017 and 2016 , respectively. The terms of this lease are evergreen as long as the ZI Partnership Agreement is in place. The Partnership recognized sales to the Company of $645 , $2,475 and $1,191 during the years ended December 31, 2018 , 2017 and 2016 . respectively. The Partnership purchases certain of its raw materials from the Company and is charged for various manufacturing costs incurred at the Company’s Kansas City production facility. The amount of these costs charged to the Partnership were $16,869 , $17,470 and $10,707 for the years ended December 31, 2018 , 2017 and 2016 , respectively. Certain administrative, marketing, engineering, management-related, and research and development services are provided to the Partnership by the Company. During the years ended December 31, 2018 , 2017 and 2016 , the Partnership was charged $12,727 , $12,248 and $8,169 , respectively, for these services. In addition, the Partnership was charged certain product demonstration costs of $1,768 , $2,175 and $1,663 during the years ended December 31, 2018 , 2017 and 2016 , respectively. These charges to the Partnership are recorded as reductions in either cost of goods sold or selling, general and administrative expenses in the consolidated statements of operations, depending on the nature of the expenditures. Other From time to time, the Company makes sales to portfolio companies of funds that are affiliated with CCMP and companies that are affiliated with INEOS Capital Partners. The Company had sales of $5,587 and $8,396 to companies affiliated with INEOS Capital Partners during the years ended December 31, 2018 and 2017 , respectively. Sales were immaterial to companies affiliated with INEOS Capital Partners during the years ended December 31, 2016 .

Quarterly Financial Summary (Un

Quarterly Financial Summary (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Summary (Unaudited)	27. Quarterly Financial Summary (Unaudited): The following tables summarize the Company’s quarterly financial results during the years ended December 31, 2018 and 2017 : 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Sales $ 366,197 $ 434,713 $ 427,203 $ 380,041 Gross profit 78,121 108,404 107,500 87,609 Operating income 28,189 49,054 48,854 57,459 Net income 556 16,159 14,436 28,470 Net income attributable to PQ Group Holdings Inc. 214 15,782 14,185 28,119 Net income per share: Basic income per share $ 0.00 $ 0.12 $ 0.11 $ 0.21 Diluted income per share $ 0.00 $ 0.12 $ 0.11 $ 0.21 Weighted average shares outstanding: Basic 133,154,144 133,222,463 133,336,352 133,765,294 Diluted 133,884,983 134,209,740 134,576,162 134,987,604 2017 First Quarter Second Quarter Third Quarter Fourth Quarter (1) Sales $ 332,931 $ 389,267 $ 391,829 $ 358,074 Gross profit 82,712 107,414 102,559 84,151 Operating income 37,652 55,080 46,385 26,771 Net income (loss) (2,315 ) (1,670 ) (3,016 ) 65,564 Net income (loss) attributable to PQ Group Holdings Inc. (2,454 ) (1,609 ) (3,345 ) 65,011 Net income (loss) per share: Basic income (loss) per share $ (0.02 ) $ (0.02 ) $ (0.03 ) $ 0.49 Diluted income (loss) per share $ (0.02 ) $ (0.02 ) $ (0.03 ) $ 0.49 Weighted average shares outstanding: Basic 103,947,888 104,015,815 104,096,837 133,138,140 Diluted 103,947,888 104,015,815 104,096,837 133,895,646 (1) Net income includes a provisional net tax benefit of $64,343 as a result of the rate reduction from the TCJA, which was enacted during the quarter ended December 31, 2017 . Refer to Note 19 of these consolidated financial statements for further information.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	28. Supplemental Cash Flow Information: The following table presents supplemental cash flow information for the Company: Years ended December 31, 2018 2017 2016 Cash paid during the year for: Income taxes, net of refunds $ 23,842 $ 29,199 $ 16,981 Interest (1) 105,057 170,131 132,579 Non-cash investing activity: Capital expenditures acquired on account but unpaid as of the year end 23,498 18,762 18,161 Non-cash financing activities: Equity consideration for the Business Combination (Note 7) — — 910,800 Debt assumed in the Business Combination (Note 7) — — 22,911 Debt assumed in the Acquisition (Note 8) — 16,609 — (1) Excludes capitalized interest and the net interest proceeds on swaps designated as net investment hedges, which are included within cash flows from investing activities in the Company’s consolidated statements of cash flows. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets as of December 31, 2018 , 2017 and 2016 to the total of the same amounts shown in the consolidated statements of cash flows for the years then ended: December 31, 2018 2017 2016 Cash and cash equivalents $ 57,854 $ 66,195 $ 70,742 Restricted cash included in prepaid and other current assets 1,872 1,048 14,335 Total cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows $ 59,726 $ 67,243 $ 85,077

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	29. Subsequent Events: On February 21, 2019, the Company announced that it will change the structure of its internal organization to create four independent businesses in order to promote increased visibility to business unit performance, optimize the Company’s product portfolio and create efficiencies. The reorganization, which will be effective as of March 1, 2019, will lead to the recognition of four operating and reportable segments as follows: • Catalyst (including the Zeolyst Joint Venture) • Performance Chemicals • Performance Materials • Refining Services Beginning with the quarter ending March 31, 2019, the segment results and disclosures will reflect the new segment structure for all periods presented. For the purposes of the Company’s goodwill impairment testing, the four new segments align with the Company’s existing reporting units at which level goodwill has been assigned and tested (see Note 14 to these consolidated financial statements for information regarding the Company’s reporting units and annual goodwill impairment test). Other than the change to the Company’s segments, the Company has evaluated subsequent events since the balance sheet date and determined that there are no additional items to disclose.

Schedule I - Condensed Financia

Schedule I - Condensed Financial Information of Parent	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Condensed Financial Information	SCHEDULE I PQ GROUP HOLDINGS INC. AND SUBSIDIARIES (PARENT) CONDENSED FINANCIAL INFORMATION CONDENSED STATEMENTS OF OPERATIONS (in thousands) Years ended 2018 2017 2016 Stock compensation expense $ 19,464 $ 8,799 $ 7,029 Equity in net (income) loss from subsidiaries (77,764 ) (66,402 ) 72,717 Net income (loss) 58,300 57,603 (79,746 ) Other comprehensive income (loss), net of tax: Pension and postretirement benefits (7,958 ) (101 ) 6,865 Net (loss) gain from hedging activities (330 ) (3,590 ) 4,557 Foreign currency translation (35,127 ) 61,713 (65,781 ) Total other comprehensive income (loss) (43,415 ) 58,022 (54,359 ) Comprehensive income (loss) $ 14,885 $ 115,625 $ (134,105 ) SCHEDULE I PQ GROUP HOLDINGS INC. AND SUBSIDIARIES (PARENT) CONDENSED FINANCIAL INFORMATION CONDENSED BALANCE SHEETS (in thousands, except share and per share amounts) December 31, December 31, ASSETS Total current assets $ — $ — Investment in subsidiaries 1,659,560 1,628,000 Total assets $ 1,659,560 $ 1,628,000 LIABILITIES Total current liabilities $ — $ — Total liabilities — — STOCKHOLDERS' EQUITY Common stock ($0.01 par); authorized shares 450,000,000; issued shares 135,758,269 and 135,244,379 on December 31, 2018 and December 31, 2017, respectively; outstanding shares 135,592,045 and 135,244,379 on December 31, 2018 and December 31, 2017, respectively 1,358 1,352 Preferred stock ($0.01 par); authorized shares 50,000,000; no shares issued or outstanding on December 31, 2018 and December 31, 2017 — — Additional paid-in capital 1,674,703 1,655,114 Retained earnings (accumulated deficit) 25,523 (32,777 ) Treasury stock, at cost; shares 166,224 and 0 on December 31, 2018 and 2017, respectively (2,920 ) — Accumulated other comprehensive (loss) income (39,104 ) 4,311 Total PQ Group Holdings Inc. equity 1,659,560 1,628,000 Total liabilities and equity $ 1,659,560 $ 1,628,000 SCHEDULE I PQ GROUP HOLDINGS INC. AND SUBSIDIARIES (PARENT) CONDENSED FINANCIAL INFORMATION CONDENSED STATEMENTS OF CASH FLOWS (in thousands) Years ended 2018 2017 2016 Cash flows from operating activities: Net income (loss) $ 58,300 $ 57,603 $ (79,746 ) Adjustments to reconcile net income (loss) to net cash provided by operating activities: Equity in net (income) loss from subsidiaries (77,764 ) (66,402 ) 72,717 Stock compensation expense 19,464 8,799 7,029 Net cash provided by operating activities — — — Cash flows from investing activities: Investment in subsidiaries — (480,696 ) — Net cash used in investing activities — (480,696 ) — Cash flows from financing activities: IPO proceeds — 507,500 — IPO costs — (26,804 ) — Net cash provided by financing activities — 480,696 — Effect of exchange rate changes on cash, cash equivalents and restricted cash — — — Net change in cash, cash equivalents and restricted cash — — — Cash, cash equivalents and restricted cash at beginning of period — — — Cash, cash equivalents and restricted cash at end of period $ — $ — $ — SCHEDULE I PQ GROUP HOLDINGS INC. AND SUBSIDIARIES (PARENT) CONDENSED FINANCIAL INFORMATION NOTES TO CONDENSED SCHEDULE I 1. Description of PQ Group Holdings Inc. and Subsidiaries On August 17, 2015, PQ Holdings Inc. (“PQ Holdings”), Eco Services Operations LLC (“Eco Services”), certain investment funds affiliated with CCMP Capital Advisors, LLC (now known as CCMP Capital Advisors, LP; “CCMP”), and stockholders of PQ Holdings and Eco Services entered into a reorganization and transaction agreement pursuant to which the companies consummated a series of transactions to reorganize and combine the businesses of PQ Holdings and Eco Services (the “Business Combination”), under a new holding company, PQ Group Holdings Inc. (“PQ Group Holdings” or the “Parent Company”). The Business Combination was consummated on May 4, 2016. In accordance with accounting principles generally accepted in the United States (“GAAP”), Eco Services is the accounting predecessor to PQ Group Holdings. Certain investment funds affiliated with CCMP held a controlling interest position in Eco Services prior to the Business Combination. In addition, certain investment funds affiliated with CCMP owned a non-controlling interest in PQ Holdings prior to the Business Combination and the merger with Eco Services constituted a change in control under the PQ Holdings credit agreements and bond indenture that were in place at the time of the Business Combination. Therefore, Eco Services is deemed to be the accounting acquirer. These Parent Company condensed financial statements are the continuation of Eco Services’ business prior to the Business Combination. PQ Group Holdings is a holding company that conducts substantially all of its business operations through its wholly owned subsidiary, PQ Corporation. As specified in certain of PQ Corporation’s debt agreements entered into concurrently with the Business Combination, there are restrictions on the ability of PQ Corporation to make payments to its stockholder, PQ Group Holdings, on behalf of their equity interests (refer to Note 16 to the PQ Group Holdings consolidated financial statements for further information regarding PQ Corporation debt). 2. Basis of Presentation The accompanying condensed Parent Company financial statements are required in accordance with Rule 4-08(e)(3) of Regulation S-X. These condensed financial statements have been presented on a “parent-only” basis. Under a parent-only presentation, the Parent Company’s investment in its consolidated subsidiary is presented under the equity method of accounting. Under the equity method, the investment in subsidiary is stated at cost plus contributions and equity in undistributed income (loss) of the subsidiary, less distributions received since the date of acquisition. For purposes of presenting net income, this presentation assumes that the Parent Company was in existence for the full year ended December 31, 2016, the year of the Business Combination. These parent-only financial statements should be read in conjunction with PQ Group Holdings’ audited consolidated financial statements. 3. Stock-Based Compensation Refer to Note 22 of the notes to the PQ Group Holdings consolidated financial statements for a description of stock-based compensation. 4. Common Stock Refer to Note 21 of the notes to the PQ Group Holdings consolidated financial statements for a description of common stock.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation PQ Merger with Eco Services On August 17, 2015, the Company, PQ Holdings Inc. (“PQ Holdings”), Eco Services Operations LLC (“Eco Services”), certain investment funds affiliated with CCMP Capital Advisors, LLC (now known as CCMP Capital Advisors, LP; “CCMP”), and stockholders of PQ Holdings and Eco Services entered into a reorganization and transaction agreement pursuant to which the companies consummated a series of transactions to reorganize and combine the businesses of PQ Holdings and Eco Services (the “Business Combination”), under a new holding company, PQ Group Holdings Inc. The Business Combination was consummated on May 4, 2016. In accordance with accounting principles generally accepted in the United States (“GAAP”), Eco Services is the accounting predecessor to PQ Group Holdings. Certain investment funds affiliated with CCMP held a controlling interest position in Eco Services prior to the Business Combination. In addition, certain investment funds affiliated with CCMP owned a non-controlling interest in PQ Holdings prior to the Business Combination and the merger with Eco Services constituted a change in control under the PQ Holdings credit agreements and bond indenture that were in place at the time of the Business Combination. Therefore, Eco Services is deemed to be the accounting acquirer. These consolidated financial statements are the continuation of Eco Services’ business prior to the Business Combination. Basis of Presentation The accompanying condensed Parent Company financial statements are required in accordance with Rule 4-08(e)(3) of Regulation S-X. These condensed financial statements have been presented on a “parent-only” basis. Under a parent-only presentation, the Parent Company’s investment in its consolidated subsidiary is presented under the equity method of accounting. Under the equity method, the investment in subsidiary is stated at cost plus contributions and equity in undistributed income (loss) of the subsidiary, less distributions received since the date of acquisition. For purposes of presenting net income, this presentation assumes that the Parent Company was in existence for the full year ended December 31, 2016, the year of the Business Combination. These parent-only financial statements should be read in conjunction with PQ Group Holdings’ audited consolidated financial statements.
Principles of Consolidation	Principles of Consolidation. The consolidated financial statements include the accounts of the Company and its controlled subsidiaries. Investments in affiliated companies are recorded at cost plus the Company’s equity in their undistributed earnings. All intercompany transactions have been eliminated. Noncontrolling interests represent third-party equity ownership in certain of the Company’s consolidated subsidiaries and are presented as a component of equity separate from the equity attributable to the Company’s shareholders. The noncontrolling interests’ share in the Company’s net earnings are included in net income attributable to the noncontrolling interest in the Company’s consolidated statements of operations, and their portion of the Company’s comprehensive income is included in comprehensive loss attributable to noncontrolling interests in the Company’s consolidated statements of comprehensive income (loss). The Company’s noncontrolling interests relate to third-party minority ownership interests held in certain of the Company’s foreign subsidiaries acquired as part of the Business Combination.
Foreign Currency Transactions and Translations Policy	Foreign Currency Translation. All assets and liabilities of foreign subsidiaries and affiliated companies are translated to U.S. dollars using exchange rates in effect at the balance sheet date. Adjustments resulting from translation of the balance sheets and intercompany loans, which are considered permanent, are included in stockholders’ equity as part of accumulated other comprehensive income (loss). Adjustments resulting from translation of certain intercompany loans, which are not considered permanent and are denominated in foreign currencies, are included in other (income) expense, net in the consolidated statements of operations. The Company considers intercompany loans to be of a permanent or long-term nature if management expects and intends that the loans will not be repaid. For the years ended December 31, 2018 , 2017 and 2016 , all intercompany loan arrangements were determined to be non-permanent based on management’s intention as well as actual lending and repayment activity. Therefore, the foreign currency transaction gains or losses associated with the intercompany loans were recorded in the consolidated statements of operations for the years ended December 31, 2018 , 2017 and 2016 . Income and expense items are translated at average exchange rates during the year. Net foreign currency exchange (gains) and losses included in other expense (income), net were $13,810 , $25,786 and $(3,558) for the years ended December 31, 2018 , 2017 and 2016 , respectively. The net foreign currency losses realized in 2018 and 2017 and gain realized in 2016 were primarily driven by the Euro-denominated term loan (which was settled as part of the February 2018 term loan refinancing, see Note 16 to these consolidated financial statements for further information) and the non-permanent intercompany debt denominated in local currency and translated to U.S. dollars.
Cash and Cash Equivalents	Cash and Cash Equivalents. Cash and cash equivalents include investments with original terms to maturity of 90 days or less from the time of purchase.
Restricted Cash	Restricted Cash. Restricted cash, which is restricted as to withdrawal or usage, is classified separately from cash and cash equivalents on our consolidated balance sheets. The proceeds from the New Markets Tax Credit (“NMTC”) financing arrangements are restricted for use and are classified on the Company’s consolidated balance sheets as other current assets. See Note 16 to these consolidated financial statements for further information regarding the NMTC financing arrangements. The Company’s total restricted cash balances, including cash related to the NMTC financing arrangements, were $1,872 and $1,048 as of December 31, 2018 and 2017 , respectively, and are included on the Company’s consolidated balance sheets as other current assets.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for Doubtful Accounts. Trade accounts receivable are recorded at the invoiced amount and do not bear interest. The allowance for doubtful accounts is the Company’s best estimate of the amount of probable credit losses in its existing accounts receivable. A specific reserve for bad debt is recorded for known or suspected doubtful accounts receivable. For all other accounts, the Company recognizes a reserve for bad debt based on the length of time receivables are past due and historical write-off experience. Account balances are charged against the allowance when the Company believes it is probable that the associated receivables will not be recovered. If the financial condition of the Company’s customers were to deteriorate resulting in an impairment of their ability to make payments, additional allowances may be required. The Company does not have any off-balance sheet credit exposure related to its customers. As of December 31, 2018 and 2017 , the Company’s allowance for doubtful accounts was not material.
Inventories	Inventories. Certain domestic inventories are stated at the lower of cost or market and valued using the last-in, first-out (“LIFO”) method. All other inventories are stated at the lower of cost and net realizable value and valued using the weighted average cost or first-in, first-out (“FIFO”) methods.
Property, Plant and Equipment	Property, Plant and Equipment. Property, plant and equipment are carried at cost and include expenditures for new facilities, major renewals and betterments. The Company capitalizes the cost of furnace rebuilds as part of property, plant and equipment. Plant and equipment under capital leases are carried at the present value of minimum lease payments as determined at the beginning of the lease term. Maintenance, repairs and minor renewals are charged to expense as incurred. The Company capitalizes certain internal costs associated with the implementation of purchased software. When property, plant and equipment is retired or otherwise disposed of, the net carrying amount is eliminated with any gain or loss on disposition recognized in earnings at that time. The Company also leases property, plant and equipment, principally under operating leases. Rent expense for operating leases, which may have escalating rentals or rent holidays, is recorded on a straight-line basis over the respective lease terms. Depreciation is provided on the straight-line method based on the estimated useful lives of the assets, which generally range from 15 to 33 years for buildings and improvements and 3 to 10 years for machinery and equipment. Leasehold improvements are depreciated using the straight-line method based on the shorter of the useful life of the improvement or remaining lease term. The Company capitalizes the interest cost associated with the development and construction of significant new plant and equipment and depreciates that amount over the lives of the related assets. Capitalized interest recorded during the years ended December 31, 2018 , 2017 and 2016 was $3,542 , $5,806 and $5,687 , respectively.
Spare Parts	Spare Parts. Spare parts are maintained by the Company’s facilities to keep machinery and equipment in working order. Spare parts are capitalized and included in other long-term assets. Spare parts are measured at cost and are not depreciated or expensed until utilized; however, reserves may be provided on aged spare parts. When a spare part is utilized as part of an improvement to property, plant and equipment, the carrying value is depreciated over the applicable life once placed in service. Otherwise, the spare part is expensed and charged as a cost of production when utilized.
Investments in Affiliated Companies	Investments in Affiliated Companies. Investments in affiliated companies are accounted for using the equity method of accounting if the investment provides the Company with the ability to exercise significant influence, but not control, over the investee. Significant influence is generally deemed to exist if the Company’s ownership interest in the voting stock of the investee ranges between 20% and 50%, although other factors, such as representation on the investee’s board of directors and the impact of commercial arrangements, are considered in determining whether the equity method of accounting is appropriate. Under the equity method of accounting, the investments in equity-method investees are recorded in the consolidated balance sheets as investments in affiliated companies, and the Company’s share of the investees’ earnings or losses, together with other-than temporary impairments in value, is recorded as equity in net income (loss) from affiliated companies in the consolidated statements of operations. Any differences between the Company’s cost of an equity method investment and the underlying equity in the net assets of the investment, such as fair value step-ups resulting from acquisitions, are accounted for according to their nature and impact the amounts recognized as equity in net income (loss) from affiliated companies in the consolidated statements of operations. The Company evaluates all distributions received from its equity method investments using the nature of distribution approach. Under this approach, the Company evaluates the nature of activities of the investee that generated the distribution. The distributions received are either classified as a return on investment, which is presented as a component of operating activities on the Company’s consolidated statements of cash flows, or as a return of investment, which is presented as a component of investing activities on the Company’s consolidated statements of cash flows. The Company evaluates its equity method investments for impairment whenever events or changes in circumstances indicate that the carrying amounts of such investments may be impaired. If a decline in the value of an equity method investment is determined to be other than temporary, a loss is recorded in earnings in the current period.
Goodwill and Intangible Assets	Goodwill and Intangible Assets. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. The Company is required to test goodwill associated with each of its reporting units for impairment at least annually and whenever events or circumstances indicate that it is more likely than not that goodwill may be impaired. The Company performs its annual goodwill impairment test as of October 1 of each year. Goodwill is tested for impairment at the reporting unit level. In performing tests for goodwill impairment, the Company is permitted to first perform a qualitative assessment about the likelihood of the carrying value of a reporting unit exceeding its fair value. If an entity determines that it is more likely than not that the fair value of a reporting unit is less than its carrying amount based on the qualitative assessment, it is required to perform a two-step goodwill impairment test to identify the potential goodwill impairment and measure the amount of the goodwill impairment loss, if any, to be recognized for that reporting unit. However, if an entity concludes otherwise based on the qualitative assessment, the two-step goodwill impairment test is not required. The option to perform the qualitative assessment can be utilized at the Company’s discretion, and the qualitative assessment need not be applied to all reporting units in a given goodwill impairment test. For an individual reporting unit, if the Company elects not to perform the qualitative assessment, or if the qualitative assessment indicates that it is more likely than not that the fair value of a reporting unit is less than its carrying amount, then the Company must perform the two-step goodwill impairment test for the reporting unit. In applying the two-step process, the first step used to identify potential impairment involves comparing the reporting unit’s estimated fair value to its carrying value, including goodwill. If the estimated fair value of a reporting unit exceeds its carrying value, goodwill is not impaired. If the carrying value exceeds the estimated fair value, there is an indication of potential impairment and the second step is performed to measure the amount of impairment, if any. The second step of the process involves the calculation of an implied fair value of goodwill for each reporting unit for which step one indicated potential impairment. The implied fair value of goodwill is determined in a manner similar to how goodwill is calculated in a business combination. That is, the estimated fair value of the reporting unit, as calculated in step one, is allocated to the individual assets and liabilities as if the reporting unit was being acquired in a business combination. If the implied fair value of goodwill exceeds the carrying value of goodwill assigned to the reporting unit, there is no impairment. If the carrying value of goodwill assigned to a reporting unit exceeds the implied fair value of the goodwill, an impairment charge is recorded to write down the carrying value. An impairment loss cannot exceed the carrying value of goodwill assigned to a reporting unit and the loss establishes a new basis in the goodwill. Subsequent reversal of an impairment loss is not permitted. For intangible assets other than goodwill, definite-lived intangible assets are amortized over their respective estimated useful lives. Intangible assets with indefinite lives are not amortized, but rather are tested for impairment at least annually or more frequently if events occur or circumstances change that would more likely than not reduce the fair value of the intangible asset below its carrying amount. The Company tests its indefinite-lived intangible assets as of October 1 of each year in conjunction with its annual goodwill impairment test.
Impairment Assessment of Long-Lived Assets	Impairment Assessment of Long-Lived Assets. The Company performs an impairment review of property, plant and equipment and definite-lived intangible assets when facts and circumstances indicate that the carrying value of an asset or asset group may not be recoverable from its undiscounted future cash flows. When evaluating long-lived assets for impairment, if the carrying amount of an asset or asset group is found not to be recoverable, a potential impairment loss may be recognized. An impairment loss is measured by comparing the carrying amount of the asset or asset group to its fair value. Fair value is determined using quoted market prices when available, or other techniques including discounted cash flows. The Company’s estimates of future cash flows involve assumptions concerning future operating performance, economic conditions and technological changes that may affect the future useful lives of the assets.
Derivative Financial Instruments	Derivative Financial Instruments. The Company utilizes certain derivative financial instruments to enhance its ability to manage risk, including exposure to interest rate, commodity price, and foreign currency fluctuations that exist as part of ongoing business operations. Derivative instruments are entered into for periods consistent with the related underlying exposures and do not constitute positions independent of those exposures. All derivatives designated as hedges are recognized on the consolidated balance sheets at fair value. The Company may designate a derivative as a hedge of the fair value of a recognized asset or liability or of an unrecognized firm commitment (fair value hedge), a hedge of a forecasted transaction or the variability of cash flows to be received or paid related to a recognized asset or liability (cash flow hedge), a foreign currency fair-value or cash-flow hedge (foreign currency hedge), or a hedge of a net investment in a foreign operation (net investment hedge). The Company’s hedging strategies include derivatives designated as cash flow hedges and net investment hedges. Changes in the fair value of a derivative that is highly effective and that is designated and qualifies as a cash flow hedge are recorded in other comprehensive income and subsequently reclassified into earnings in the same period(s) in which the hedged transaction affects earnings. Changes in the fair value of a derivative that is highly effective and that is designated and qualifies as a hedge of a net investment in a foreign operation are recorded in the foreign currency translation adjustment account within accumulated other comprehensive income, where the associated gains and losses will remain until such time that the hedged net investment (foreign subsidiary) is sold or liquidated. Changes in the fair value of a derivative that is not designated or does not qualify as a hedge are recorded in the consolidated statements of operations. Cash flows from derivative instruments are reported in the same cash flow category as the cash flows from the items being hedged. The Company formally documents all relationships between hedging instruments and hedged items, as well as its risk-management objective and strategy for undertaking various hedge transactions. The Company also formally assesses whether each hedging relationship is highly effective in achieving offsetting changes in fair values or cash flows of the hedged item during the period, both at the inception of the hedge and on an ongoing basis. If it is determined that a derivative is not highly effective as a hedge, or if a derivative ceases to be a highly-effective hedge, hedge accounting is discontinued with respect to that derivative prospectively.
Fair Value Measurement	The carrying values of cash, accounts receivable, accounts payable and accrued liabilities approximate fair value due to the short-term nature of these items. Fair Value Measurements. The Company measures fair value using the guidelines under GAAP. An asset’s fair value is defined as the price at which the asset could be exchanged in a current transaction between market participants. A liability’s fair value is defined as the amount that would be paid to transfer the liability to a market participant, not the amount that would be paid to settle the liability with the creditor. See Note 5 to these consolidated financial statements regarding the application of fair value measurements. The carrying values of cash, accounts receivable, accounts payable and accrued liabilities approximate fair value due to the short-term nature of these items. See Note 16 to these consolidated financial statements regarding the fair value of debt. Restoration plan assets The fair values of the Company’s restoration plan assets are determined through quoted prices in active markets. Restoration plan assets are assets held in a Rabbi trust to fund the obligations of the Company’s defined benefit supplementary retirement plans and include various stock and fixed income mutual funds. See Note 20 to these consolidated financial statements regarding defined benefit supplementary retirement plans. The Company’s restoration plan assets are included in other long-term assets on its consolidated balance sheets. Gains and losses related to these investments are included in other expense, net in the Company’s consolidated statements of operations. Unrealized gains and losses associated with the underlying stock and fixed income mutual funds were immaterial as of December 31, 2018 and December 31, 2017 , respectively. Derivative contracts Derivative assets and liabilities can be exchange-traded or traded over-the-counter (“OTC”). The Company generally values exchange-traded derivatives using models that calibrate to market transactions and eliminate timing differences between the closing price of the exchange-traded derivatives and their underlying instruments. OTC derivatives are valued using market transactions and other market evidence whenever possible, including market-based inputs to models, model calibration to market transactions, broker or dealer quotations or alternative pricing sources with reasonable levels of price transparency. When models are used, the selection of a particular model to value an OTC derivative depends on the contractual terms of, and specific risks inherent in, the instrument as well as the availability of pricing information in the market. The Company generally uses similar models to value similar instruments. Valuation models require a variety of inputs, including contractual terms, market prices and rates, forward curves, measures of volatility, and correlations of such inputs. For OTC derivatives that trade in liquid markets, such as forward contracts, swaps and options, model inputs can generally be corroborated by observable market data by correlation or other means, and model selection does not involve significant management judgment. The Company has interest rate caps, natural gas swaps and cross currency swaps that are fair valued using Level 2 inputs. In addition, the Company applies a credit valuation adjustment to reflect credit risk which is calculated based on credit default swaps. To the extent that the Company’s net exposure under a specific master agreement is an asset, the Company utilizes the counterparty’s default swap rate. If the net exposure under a specific master agreement is a liability, the Company utilizes a default swap rate comparable to PQ Group Holdings. The credit valuation adjustment is added to the discounted fair value to reflect the exit price that a market participant would be willing to receive to assume the Company’s liabilities or that a market participant would be willing to pay for the Company’s assets.
Revenue Recognition	Revenue Recognition. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under its agreements, the Company performs the following steps: (i) identification of the contract with the customer; (ii) determination of whether the promised goods or services are performance obligations, including whether they are distinct in the context of the contract; (iii) measurement of the transaction price; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company identifies a contract when an agreement with a customer creates legally enforceable rights and obligations, which occurs when a contract has been approved by both parties, the parties are committed to perform their respective obligations, each party’s rights and payment terms are clearly identified, commercial substance exists and it is probable that the Company will collect the consideration to which it is entitled. The Company may offer rebates to customers who have reached a specified volume of optional purchases. The Company recognizes rebates given to customers as a reduction of revenue based on an allocation of the cost of honoring rebates earned and claimed to each of the underlying revenue transactions that result in progress by the customer toward earning the rebate. Rebates are recognized at the time revenue is recorded. The Company measures the rebate obligation based on the estimated amount of sales that will result in a rebate at the adjusted sales price per the respective sales agreement.
Shipping and Handling Costs	Shipping and Handling Costs. Amounts billed to a customer in a sale transaction related to shipping and handling, if any, represent revenues earned for the goods provided and are classified as revenue. Costs related to shipping and handling of products shipped to customers are classified as cost of goods sold. Refer to Note 4 for disclosures regarding the recognition of revenue for shipping and handling costs that are billed to customers.
Research and Development	Research and Development. Research and development costs of $15,565 , $13,859 and $7,266 for the years ended December 31, 2018 , 2017 and 2016 , respectively, were expensed as incurred and reported in selling, general and administrative expenses in the consolidated statements of operations.
Income Taxes	Income Taxes. Prior to the Business Combination, Eco Services was a single member limited liability company and was treated as a partnership for federal and state tax purposes. All income tax liabilities and/or benefits of the Company were passed through to the member. As such, no recognition of federal or state income taxes for the Company have been provided for tax periods prior to the Business Combination. As a result of the Business Combination, Eco Services had a change in tax status and is taxed as a C-Corporation. The Company operates within multiple taxing jurisdictions and are subject to tax filing requirements and audit within these jurisdictions. The Company uses the asset and liability method in accounting for income taxes. Deferred tax assets and liabilities are recorded for temporary differences between the tax basis of assets and liabilities and their reported amounts in the financial statements, using statutory tax rates in effect for the year in which the differences are expected to reverse. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in the results of operations in the period that includes the enactment date. The Company evaluates its deferred tax assets each period to ensure that estimated future taxable income will be sufficient in character (e.g., capital gain versus ordinary income treatment), amount and timing to result in their recovery. A valuation allowance is recorded to reduce the carrying amounts of deferred tax assets unless it is more likely than not that those assets will be realized. In determining the provision for income taxes, the Company provides deferred income taxes on income from foreign subsidiaries as such earnings are taxable upon remittance to the United States, to the extent that these earnings are considered to be available for repatriation. The Company does not provide income taxes on the cumulative unremitted earnings of foreign subsidiaries considered permanently reinvested. The Company establishes contingent liabilities for possible assessments by taxing authorities resulting from uncertain tax positions including, but not limited to, transfer pricing, deductibility of certain expenses and other state, local, and foreign tax matters. The Company recognizes a financial statement benefit for positions taken for tax return purposes when it will be more likely than not (greater than 50%) that the positions will be sustained upon tax examination, based solely on the technical merits of the tax positions, otherwise, no benefit is recognized. The tax benefits recognized are measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. The Company recognizes potential accrued interest and penalties related to unrecognized tax benefits in income tax expense. Tax examinations are often complex as tax authorities may disagree with the treatment of items reported by the Company and may require several years to resolve. These accrued liabilities represent a provision for taxes that are reasonably expected to be incurred on the basis of available information but which are not certain. Pursuant to the Securities and Exchange Commission (“SEC”) Staff Accounting Bulletin No.118 (“SAB 118”), the Company was allowed a measurement period of up to one year after the enactment date of the Tax Cuts and Jobs Act (“TCJA”) to finalize the recording of any related tax impacts with respect to its transition tax liability. As of December 31, 2017 , the Company’s accounting for these impacts was provisional. However, in accordance with SAB 118, the Company has finalized the impacts of the transition tax as of December 31, 2018 and has recorded a measurement period adjustment of $2,102 as a benefit to tax expense. There was no cash tax outlay associated with the final transition tax amount, as the Company elected to utilize net operating loss (“NOL”) carryforwards to offset the associated taxable income. Based on FASB guidance, the Company is permitted to make an accounting policy election to either (1) treat the taxes incurred as a result of the GILTI provision as a current-period expense when incurred or (2) factor such amounts into its measurement of deferred taxes. The Company has elected to treat any expense incurred as a current-period expense.
Asset Retirement Obligations	Asset Retirement Obligations. The Company records a liability when the fair value of any future obligation to retire a long-lived asset as a result of an existing or enacted law, statute, ordinance or contract is reasonably estimable. The Company also records a liability for the fair value of a conditional asset retirement obligation if the fair value can be reasonably estimated. When the liability is initially recorded, the Company capitalizes the cost by increasing the amount of the related long-lived asset. Over time, the Company adjusts the liability to its present value by recognizing accretion expense as an operating expense in the consolidated statements of operations each period, and the capitalized cost is depreciated over the useful life of the related asset. Upon settlement of the liability, the Company records a gain or loss if the actual costs differ from the accrued amount.
Environmental Expenditures	Environmental Expenditures. Environmental expenditures that pertain to current operations or to future revenues are expensed or capitalized consistent with the Company’s capitalization policy for property, plant and equipment. Expenditures that result from the remediation of an existing condition caused by past operations and that do not contribute to current or future revenues are expensed. Liabilities are recognized for remedial activities when the remediation is probable and the cost can be reasonably estimated. Recoveries of expenditures for environmental remediation are recognized as assets only when recovery is deemed probable. See Note 23 to these consolidated financial statements regarding commitments and contingencies and Note 15 regarding the accrued environmental reserve.
Deferred Finance Costs	Deferred Financing Costs. Financing costs incurred in connection with the issuance of long-term debt are deferred and presented as a direct reduction from the related debt instruments on the Company’s consolidated balance sheets. Deferred financing costs are amortized as interest expense using the effective interest method over the respective terms of the associated debt instruments.
Stock-Based Compensation	Stock-Based Compensation. The Company applies the fair value based method to account for stock options, restricted stock awards and restricted stock units issued in connection with its equity incentive plans. Stock-based compensation expense is recognized on a straight-line basis over the vesting periods of the respective awards, and the Company accounts for forfeitures of equity incentive awards as they occur. In connection with the vesting of restricted stock awards and restricted stock units, shares of common stock may be delivered to the Company by employees to satisfy withholding tax obligations at the instruction of the employee award holders. These transactions when they occur are accounted for as stock repurchases by the Company, with the shares returned to treasury stock at a cost representing the payment by the Company of the tax obligations on behalf of the employees in lieu of shares for the vesting event. See Note 22 to these consolidated financial statements regarding compensation expense associated with the Company’s equity incentive awards.
Pensions and Postretirement Benefits	Pensions and Postretirement Benefits. The Company maintains qualified and non-qualified defined benefit pension plans that cover employees in the United States and Canada, as well as certain employees in other international locations. Benefits for a majority of the plans are based on average final pay and years of service. Our funding policy, consistent with statutory requirements, is based on actuarial computations utilizing the projected unit credit method of calculation. Not all defined benefit pension plans are funded. In the United States and Canada, the pension plans’ assets include equity and fixed income securities. In our other international locations, the pension plans’ assets include equity and fixed income securities, as well as insurance contracts. Certain assumptions are made regarding the occurrence of future events affecting pension costs, such as mortality, withdrawal, disablement and retirement, changes in compensation and benefits, and discount rates to reflect the time value of money. The major elements in determining pension income and expense are pension liability discount rates and the expected return on plan assets. The Company references rates of return on high-quality, fixed income investments when estimating the discount rate, and the expected period over which payments will be made based upon historical experience. The long-term rate of return used to calculate the expected return on plan assets is the average rate of return estimated to be earned on invested funds for providing pension benefits. In addition to pension benefits, the Company provides certain health care benefits for employees who meet age, participation and length of service requirements at retirement. The Company uses explicit assumptions using the best estimates available of the plan’s future experience. Principal actuarial assumptions include: discount rates, present value factors, retirement age, participation rates, mortality rates, cost trend rates, Medicare reimbursement rates and per capita claims cost by age. Current interest rates as of the measurement date are used for discount rates in present value calculations. The Company also has defined contribution plans covering domestic employees of the Company and certain subsidiaries.
Contingencies	Contingencies. Certain conditions may exist as of the date the financial statements are issued, which may result in a loss to the Company but which will only be resolved when one or more future events occur or fail to occur. The Company’s management and its legal counsel assess such contingent liabilities, and such assessment inherently involves an exercise of judgment. In assessing loss contingencies related to legal proceedings that are pending against the Company or unasserted claims that may result in such proceedings, the Company and legal counsel evaluate the perceived merits of any legal proceedings or unasserted claims as well as the perceived merits of the amount of relief sought or expected to be sought therein. If the assessment of a contingency indicates that it is probable that a loss has been incurred and the amount of the liability can be estimated, then the estimated liability is accrued in the Company’s financial statements. If the assessment indicates that a loss contingency is not probable, but is reasonably possible, or is probable but cannot be estimated, then the nature of the contingent liability, together with an estimate of the range of possible loss if determinable and material, would be disclosed. Loss contingencies considered remote are generally not disclosed unless they involve guarantees, in which case the nature of the guarantee would be disclosed, including the approximate term, how the guarantee arose, and the events or circumstances that would require the guarantor to perform under the guarantee.
Use of Estimates	Use of Estimates. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Recently Issued Accounting Standards	Recently Adopted Accounting Standards In August 2018, the Financial Accounting Standards Board (“FASB”) issued guidance which will align the requirements for capitalizing implementation costs incurred in a cloud computing arrangement (i.e., a hosting arrangement) that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. Capitalized implementation costs related to a hosting arrangement that is a service contract will be amortized over the term of the hosting arrangement, beginning when the module or component of the hosting arrangement is ready for its intended use. The guidance is effective for public companies for fiscal years beginning after December 15, 2019, including all interim periods within that fiscal year. Early adoption is permitted, and the guidance can be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. The Company early adopted the guidance effective October 1, 2018 and has applied the guidance on a prospective basis for any implementation costs incurred subsequent to the adoption date, with no significant impact on the Company’s consolidated financial statements. In August 2017, the FASB issued amendments related to hedge accounting. The amendments expand hedge accounting for non-financial and financial risk components and revise the measurement methodologies to better align with an entity’s risk management activities. Separate presentation of hedge ineffectiveness is eliminated to provide greater transparency of the full impact of hedging by requiring presentation of the results of the hedged item and hedging instrument in a single financial statement line item. In addition, the amendments reduce complexity by simplifying the manner in which assessments of hedge effectiveness may be performed. The new guidance is effective for public companies for annual periods beginning after December 15, 2018, including interim periods within those years. Early adoption is permitted, and the guidance should be applied prospectively for the amended presentation and disclosure requirements, and through a cumulative-effect adjustment to beginning retained earnings for any cash flow and net investment hedges existing at the date of adoption. The Company early adopted the guidance effective January 1, 2018. The Company’s cash flow hedges in place at the date of adoption yielded an immaterial amount of ineffectiveness; therefore, the Company did not reflect an adjustment to beginning retained earnings upon adoption. The amended presentation and disclosure requirements are reflected under the new guidance in Note 18 to these consolidated financial statements. In May 2017, the FASB issued guidance to clarify which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting. Under the new guidance, an entity should account for the effects of a change in a share-based payment award using modification accounting unless the fair value, vesting conditions and classification as either a liability or equity are all the same with respect to the award immediately prior to modification and the modified award itself. The new guidance is effective for annual periods beginning after December 15, 2017, including interim periods within those years, and the new guidance should be applied prospectively to awards modified on or after the adoption date. The Company adopted the new guidance on January 1, 2018 as required, with no impact on the Company’s consolidated financial statements upon adoption. In March 2017, the FASB issued guidance to improve the presentation of net periodic pension cost and net periodic postretirement benefit cost (collectively, “pension costs”). Under current GAAP, there are several components of pension costs which are presented net to arrive at pension costs as included in the income statement and disclosed in the notes. As part of this amendment to the existing guidance, the service cost component of pension costs will be bifurcated from the other components and included in the same line items of the income statement as compensation costs are reported. The remaining components will be reported together below operating income on the income statement, either as a separate line item or combined with another line item on the income statement and disclosed. Additionally, with respect to capitalization to inventory, fixed assets, etc., only the service cost component will be eligible for capitalization upon adoption of the guidance. The new guidance is effective for public companies for annual periods beginning after December 15, 2017, including interim periods within those years. The amendments should be applied retrospectively upon adoption with respect to the presentation of the service and other cost components of pension costs in the income statement, and prospectively for the capitalization of the service cost component in assets. The Company adopted the new guidance on January 1, 2018 as required. Prior to the adoption of the guidance, the Company reflected its pension costs within cost of goods sold and selling, general and administrative expenses in the consolidated statements of operations, depending on whether the costs were associated with employees involved in manufacturing or back office support functions. Under the new guidance, the service cost component of the Company’s pension costs remained in the same line items of the consolidated statements of operations, but the remaining components are now reported as part of nonoperating income in the other (income) expense, net line item of the consolidated statements of operations. Although the guidance requires retrospective application upon adoption, a practical expedient permits the Company to use the amounts disclosed in its pension and other post-retirement benefit plan note as its basis of estimation for the prior comparative periods. The Company utilized the practical expedient, and $1,616 and $2,651 of a net pension benefit for the years ended December 31, 2017 and 2016 , respectively, was reclassified to other expense (income), net. For the year ended December 31, 2018 , the amount of pension costs included in other expense (income), net was a net benefit of $3,625 . In January 2017, the FASB issued guidance that clarifies the definition of a business and provides revised criteria and a framework to determine whether an integrated set of assets and activities is a business. For public companies, the new guidance is effective for fiscal years beginning after December 15, 2017, including interim periods within those years. The Company adopted the new guidance on January 1, 2018 as required, with no impact on the Company’s consolidated financial statements upon adoption. In November 2016, the FASB issued guidance which clarifies the classification and presentation of changes in restricted cash on the statement of cash flows. The updates in the guidance require that the statement of cash flows explain the change during the period in the total of cash, cash equivalents and restricted cash when reconciling the beginning-of-period and end-of-period total amounts. The updates also require a reconciliation between cash, cash equivalents and restricted cash presented on the balance sheet to the total of the same amounts presented on the statement of cash flows. For public companies, the new guidance is effective for fiscal years beginning after December 15, 2017 and interim periods within those years, and the new guidance should be applied retrospectively to each period presented. The Company adopted the new guidance on January 1, 2018 as required. As of December 31, 2018 and 2017 , the Company had $1,872 and $1,048 , respectively, of restricted cash included in prepaid and other current assets on its consolidated balance sheets. Changes in the Company’s restricted cash balances prior to the adoption of the new guidance were reflected within cash flows from investing activities in the Company’s consolidated statements of cash flows. The prior comparative periods in the Company’s consolidated statements of cash flows have been updated to conform to the new guidance. See Note 28 to these consolidated financial statements for supplemental cash flow disclosures. In August 2016, the FASB issued guidance which clarifies the classification of certain cash receipts and cash payments in the statement of cash flows, including debt prepayment or extinguishment costs and distributions from equity method investees. For public companies, the new guidance is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, and the new guidance should be applied retrospectively to each period presented. The Company adopted the new guidance on January 1, 2018 as required. The Company applied the new guidance to the term loan refinancing that occurred during the year ended December 31, 2018 ; see Note 16 to these consolidated financial statements for further information on the debt refinancing transaction. The following is a summary of the impact of adopting the new statement of cash flows guidance on the Company’s consolidated statements of cash flows: Year ended December 31, 2017 Previously Reported Adjustments Revised Net cash provided by operating activities (1) $ 116,062 $ 49,111 $ 165,173 Net cash used in investing activities (2) (182,695 ) (13,287 ) (195,982 ) Net cash provided by (used in) financing activities (1) 68,944 (49,111 ) 19,833 Effect of exchange rate changes on cash, cash equivalents and restricted cash (6,858 ) — (6,858 ) Net change in cash, cash equivalents and restricted cash (2) (4,547 ) (13,287 ) (17,834 ) Cash, cash equivalents and restricted cash at beginning of period (2) 70,742 14,335 85,077 Cash, cash equivalents and restricted cash at end of period (2) $ 66,195 $ 1,048 $ 67,243 Year ended December 31, 2016 Previously Reported Adjustments Revised Net cash provided by operating activities (1) $ 119,720 $ 2,988 $ 122,708 Net cash provided by (used in) investing activities (2) (1,929,680 ) 13,917 (1,915,763 ) Net cash provided by (used in) financing activities (1) 1,861,433 (2,988 ) 1,858,445 Effect of exchange rate changes on cash, cash equivalents and restricted cash (5,886 ) — (5,886 ) Net change in cash, cash equivalents and restricted cash (2) 45,587 13,917 59,504 Cash, cash equivalents and restricted cash at beginning of period (2) 25,155 418 25,573 Cash, cash equivalents and restricted cash at end of period (2) $ 70,742 $ 14,335 $ 85,077 (1) Adjustments include the reclassification of $47,875 in debt prepayment penalties for the year ended December 31, 2017, which were paid in cash, that were associated with the Company’s repricing and refinancing activities. The adjustments also include the reclassification of $1,236 and $2,988 in third-party lender fees for the years ended December 31, 2017 and 2016, respectively, associated with the Company’s repricing and refinancing activities that were paid in cash. In accordance with the August 2016 guidance which clarifies the classification of certain cash receipts and cash payments in the statement of cash flows, the amounts were reclassified from net cash provided by operating activities to net cash provided by (used in) financing activities. (2) In accordance with the November 2016 guidance that clarified the classification and presentation of changes in restricted cash on the statement of cash flows, the Company reclassified the changes in restricted cash for the respective periods from cash from investing activities to the cash, cash equivalents and restricted cash line item. In May 2014, the FASB issued accounting guidance (with subsequent targeted amendments) to significantly enhance comparability of revenue recognition practices across entities, industries, jurisdictions and capital markets. The core principle of the guidance is that revenue recognized from a transaction or event that arises from a contract with a customer should reflect the consideration to which an entity expects to be entitled in exchange for goods or services provided. To achieve that core principle, the new guidance sets forth a five-step revenue recognition model that will need to be applied consistently to all contracts with customers, except those that are within the scope of other topics in the Accounting Standards Codification (“ASC”). Also required are enhanced disclosures to help users of financial statements better understand the nature, amount, timing and uncertainty of revenues and cash flows from contracts with customers. The enhanced disclosures include qualitative and quantitative information about contracts with customers, significant judgments made in applying the revenue guidance, and assets recognized related to the costs to obtain or fulfill a contract. For public companies, the new requirements are effective for annual reporting periods beginning after December 15, 2017, including interim periods within those years. The Company reviewed its key revenue streams and assessed the underlying customer contracts within the framework of the new guidance. The Company evaluated the key aspects of its revenue streams for impact under the new guidance and performed a detailed analysis of its customer agreements to quantify the changes under the guidance. The Company concluded that the guidance did not have a material impact on its existing revenue recognition practices upon adoption on January 1, 2018. The Company implemented the guidance under the modified retrospective transition method of adoption. Comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. The impact of adoption of the new revenue recognition guidance was immaterial for the year ended December 31, 2018 , and there was no transition adjustment required upon adoption. See Note 4 to these consolidated financial statements for additional disclosures required by the new guidance. Accounting Standards Not Yet Adopted as of December 31, 2018 In August 2018, the FASB issued guidance which modifies the disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans. The guidance eliminates certain disclosure requirements, including the amounts in accumulated other comprehensive income expected to be recognized as components of net periodic benefit cost over the next fiscal year and the effects of a one-percentage point change in assumed health care cost trend rates. The guidance also requires additional disclosure of the reasons for significant gains and losses related to changes in the benefit obligation for the period. The guidance is effective for fiscal years ending after December 15, 2020 with early adoption permitted, and is required to be applied on a retrospective basis to all periods presented. The Company will modify its benefit plan disclosures in accordance with the new guidance upon adoption, and the guidance will not have a material impact on its consolidated financial statements. In August 2018, the FASB issued guidance which modifies certain disclosure requirements over fair value measurements. The guidance is effective for fiscal years beginning after December 15, 2019, including all interim periods within that fiscal year. The Company believes that the new guidance will not have a material impact on its consolidated financial statements. In June 2018, the FASB issued guidance which conforms the accounting for the issuance of all share-based payments using the same accounting model. Previously, the accounting for share-based payments to non-employees was covered under a different framework than those made to employees. Under the new guidance, awards to both employees and non-employees will essentially follow the same model, with small variations related to determining the term assumption when valuing a non-employee award as well as a different expense attribution model for non-employee awards. The new guidance is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. The Company is currently evaluating the effect that the new guidance would have on its consolidated financial statements. In February 2018, the FASB issued guidance which will permit entities to make an election to reclassify income tax effects stranded in accumulated other comprehensive income (“AOCI”) to retained earnings as a result of tax reform legislation enacted by the U.S. government on December 22, 2017. The standard is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years, with early adoption permitted in any interim period for which the financial statements have not yet been issued. Prior to the enactment of the tax reform legislation on December 22, 2017, the Company had amounts recorded in AOCI related to its domestic pension, postretirement and supplementary benefit plans and cash flow hedging relationships that were based on pre-enactment tax rates. The Company is evaluating the impact that the new guidance will have on its consolidated financial statements. If the Company makes the election to reclassify the stranded income tax effects from AOCI, it may do so using one of two transition methods: retrospectively, or at the beginning of the period of adoption. In January 2017, the FASB issued guidance which eliminates the second step from the traditional two-step goodwill impairment test. Under current guidance, an entity performed the first step of the goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount; if an impairment loss was indicated, the entity computed the implied fair value of goodwill to determine whether an impairment loss existed, and if so, the amount to recognize. Under the new guidance, an impairment loss is recognized for the amount by which the carrying amount exceeds the reporting unit’s fair value (the Step 1 test), with no further testing required. Any impairment loss recognized is limited to the amount of goodwill allocated to the reporting unit. The new guidance is effective for public companies that are Securities and Exchange Commission (“SEC”) registrants for fiscal years beginning after December 15, 2019, with early adoption permitted for goodwill impairment tests performed on testing dates after January 1, 2017. The Company will apply the guidance prospectively to goodwill impairment tests subsequent to the adoption date. In June 2016, the FASB issued guidance that affects loans, trade receivables and any other financial assets that have the contractual right to receive cash. Under the new guidance, an entity is required to recognize expected credit losses rather than incurred losses for financial assets. The new guidance is effective for fiscal years beginning after December 15, 2019 and interim periods within those fiscal years. The Company believes that the new guidance will not have a material impact on its consolidated financial statements. In February 2016, the FASB issued guidance (with subsequent targeted amendments) that modifies the accounting for leases. Under the new guidance, a lessee will recognize assets and liabilities for most leases (including those classified under existing GAAP as operating leases, which based on current standards are not reflected on the balance sheet), but will recognize expenses similar to current lease accounting. The new guidance also requires companies to provide expanded disclosures regarding leasing arrangements. For public companies, the new guidance is effective for fiscal years beginning after December 15, 2018, including interim periods within those years, with early adoption permitted. The new guidance must be adopted using a modified retrospective transition method. The Company can choose to apply the new guidance at the beginning of the earliest period presented in the financial statements, or at the date of adoption, with a cumulative-effect adjustment to the opening balance of retained earnings and no recast of prior period results presented within the Company’s consolidated financial statements. The Company has elected to apply the new guidance as of the date of adoption. The Company has operating lease agreements for which it expects to recognize right of use assets and corresponding liabilities on its balance sheet upon adoption of the new guidance. The Company is currently finalizing its lease portfolio analysis which will result in a material increase in total assets and liabilities in its consolidated balance sheets. The Company does not believe that the new guidance will have a material impact on its results of operations or cash flows. In addition, the Company has implemented a lease technology software to assist in its ongoing lease data collection and analysis. The Company is also updating its processes, accounting policies and internal controls to ensure it will meet the requirements of the new guidance upon adoption. The new guidance provides practical expedients, which the Company is currently finalizing its evaluation. The Company has elected the short term lease accounting policy and will not record right of use assets or lease liabilities for leases with a term of twelve months or less. The Company has elected the package of practical expedients which provides for an entity not to reassess: (1) whether any expired or existing contracts are, or contain, leases; (2) the lease clarification for any expired or existing leases; and (3) initial direct costs for any existing leases.

Schedule I - Condensed Financ_2

Schedule I - Condensed Financial Information of Parent (Policies)	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Basis of Presentation	Basis of Presentation PQ Merger with Eco Services On August 17, 2015, the Company, PQ Holdings Inc. (“PQ Holdings”), Eco Services Operations LLC (“Eco Services”), certain investment funds affiliated with CCMP Capital Advisors, LLC (now known as CCMP Capital Advisors, LP; “CCMP”), and stockholders of PQ Holdings and Eco Services entered into a reorganization and transaction agreement pursuant to which the companies consummated a series of transactions to reorganize and combine the businesses of PQ Holdings and Eco Services (the “Business Combination”), under a new holding company, PQ Group Holdings Inc. The Business Combination was consummated on May 4, 2016. In accordance with accounting principles generally accepted in the United States (“GAAP”), Eco Services is the accounting predecessor to PQ Group Holdings. Certain investment funds affiliated with CCMP held a controlling interest position in Eco Services prior to the Business Combination. In addition, certain investment funds affiliated with CCMP owned a non-controlling interest in PQ Holdings prior to the Business Combination and the merger with Eco Services constituted a change in control under the PQ Holdings credit agreements and bond indenture that were in place at the time of the Business Combination. Therefore, Eco Services is deemed to be the accounting acquirer. These consolidated financial statements are the continuation of Eco Services’ business prior to the Business Combination. Basis of Presentation The accompanying condensed Parent Company financial statements are required in accordance with Rule 4-08(e)(3) of Regulation S-X. These condensed financial statements have been presented on a “parent-only” basis. Under a parent-only presentation, the Parent Company’s investment in its consolidated subsidiary is presented under the equity method of accounting. Under the equity method, the investment in subsidiary is stated at cost plus contributions and equity in undistributed income (loss) of the subsidiary, less distributions received since the date of acquisition. For purposes of presenting net income, this presentation assumes that the Parent Company was in existence for the full year ended December 31, 2016, the year of the Business Combination. These parent-only financial statements should be read in conjunction with PQ Group Holdings’ audited consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of Change in Asset Retirement Obligation	The following table includes the changes in the Company’s ARO liability during the years ended December 31, 2018 and 2017 : Years ended 2018 2017 Beginning balance $ 4,094 $ 3,700 Accretion expense 287 232 Foreign exchange impact (157 ) 162 Ending balance $ 4,224 $ 4,094

New Accounting Standards (Table

New Accounting Standards (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Changes and Error Corrections [Abstract]
Adjustments to Prior Periods due to New Accounting Standards	The following is a summary of the impact of adopting the new statement of cash flows guidance on the Company’s consolidated statements of cash flows: Year ended December 31, 2017 Previously Reported Adjustments Revised Net cash provided by operating activities (1) $ 116,062 $ 49,111 $ 165,173 Net cash used in investing activities (2) (182,695 ) (13,287 ) (195,982 ) Net cash provided by (used in) financing activities (1) 68,944 (49,111 ) 19,833 Effect of exchange rate changes on cash, cash equivalents and restricted cash (6,858 ) — (6,858 ) Net change in cash, cash equivalents and restricted cash (2) (4,547 ) (13,287 ) (17,834 ) Cash, cash equivalents and restricted cash at beginning of period (2) 70,742 14,335 85,077 Cash, cash equivalents and restricted cash at end of period (2) $ 66,195 $ 1,048 $ 67,243 Year ended December 31, 2016 Previously Reported Adjustments Revised Net cash provided by operating activities (1) $ 119,720 $ 2,988 $ 122,708 Net cash provided by (used in) investing activities (2) (1,929,680 ) 13,917 (1,915,763 ) Net cash provided by (used in) financing activities (1) 1,861,433 (2,988 ) 1,858,445 Effect of exchange rate changes on cash, cash equivalents and restricted cash (5,886 ) — (5,886 ) Net change in cash, cash equivalents and restricted cash (2) 45,587 13,917 59,504 Cash, cash equivalents and restricted cash at beginning of period (2) 25,155 418 25,573 Cash, cash equivalents and restricted cash at end of period (2) $ 70,742 $ 14,335 $ 85,077 (1) Adjustments include the reclassification of $47,875 in debt prepayment penalties for the year ended December 31, 2017, which were paid in cash, that were associated with the Company’s repricing and refinancing activities. The adjustments also include the reclassification of $1,236 and $2,988 in third-party lender fees for the years ended December 31, 2017 and 2016, respectively, associated with the Company’s repricing and refinancing activities that were paid in cash. In accordance with the August 2016 guidance which clarifies the classification of certain cash receipts and cash payments in the statement of cash flows, the amounts were reclassified from net cash provided by operating activities to net cash provided by (used in) financing activities. (2) In accordance with the November 2016 guidance that clarified the classification and presentation of changes in restricted cash on the statement of cash flows, the Company reclassified the changes in restricted cash for the respective periods from cash from investing activities to the cash, cash equivalents and restricted cash line item.

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contracts with Customers [Abstract]
Disaggregation of Revenue	The Company’s portfolio of products are integrated into a variety of end uses, which are described in the table below. Key End Uses Key Products Industrial & process chemicals • Silicate precursors for the tire industry • Glass beads, or microspheres, for metal finishing end uses Fuels & emission control • Refinery catalysts • Emission control catalysts • Catalyst recycling services • Silicate for catalyst manufacturing Packaging & engineered plastics • Catalysts for high-density polyethlene and chemicals syntheses • Antiblocks for film packaging • Solid and hollow microspheres for composite plastics • Sulfur derivatives for nylon production Highway safety & construction • Reflective markings for roadways and airports • Silica gels for surface coatings Consumer products • Silica gels for edible oil and beer clarification • Precipitated silicas, silicates and zeolites for the dentifrice and dishwasher and laundry detergent applications Natural resources • Silicates for drilling muds • Hollow glass beads, or microspheres, for oil well cements • Silicates and alum for water treatment mining • Bleaching aids for paper The following table disaggregates the Company’s sales, by segment and end use, for the year ended December 31, 2018 : Environmental Catalysts & Services Performance Materials & Chemicals Total Industrial & process chemicals $ 77,952 $ 279,678 $ 357,630 Fuels & emission control (1) 246,452 — 246,452 Packaging & engineered plastics 131,181 130,996 262,177 Highway safety & construction (1) — 320,134 320,134 Consumer products — 272,576 272,576 Natural resources 72,076 80,432 152,508 Total segment sales 527,661 1,083,816 1,611,477 Inter-segment sales eliminations (3,323 ) — (3,323 ) Total $ 524,338 $ 1,083,816 $ 1,608,154 (1) As described in Note 1 , the Company experiences seasonal sales fluctuations to customers in the fuels & emission control and highway safety & construction end uses.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements, Recurring	The following table presents information about the Company’s assets and liabilities that were measured at fair value on a recurring basis as of December 31, 2018 and 2017 , and indicates the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value. December 31, 2018 Quoted Prices in Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Derivative contracts $ 20,768 $ — $ 20,768 $ — Restoration plan assets 4,244 4,244 — — Total $ 25,012 $ 4,244 $ 20,768 $ — Liabilities: Derivative contracts $ 2,026 $ — $ 2,026 $ — December 31, Quoted Prices in Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Derivative contracts $ 1,043 $ — $ 1,043 $ — Restoration plan assets 5,576 5,576 — — Total $ 6,619 $ 5,576 $ 1,043 $ — Liabilities: Derivative contracts $ 448 $ — $ 448 $ —
Fair Value Measurements, Nonrecurring	The following table presents information about the Company’s assets and liabilities that were measured at fair value on a non-recurring basis as of December 31, 2016 . The Company performed its annual impairment test on its indefinite-lived intangible assets on October 1, 2018 and 2017 , respectively, and determined that no impairment existed. Refer to Note 14 to these consolidated financial statements for a description of the valuation techniques the Company utilized to determine such fair value and for the results of the impairment testing procedures performed during the October 1, 2016 testing period. As of Quoted Prices in Significant Other Significant Total Assets: Indefinite-lived trade names (1) $ 153,922 $ — $ — $ 153,922 $ (6,873 ) (1) Indefinite-lived trade names with a carrying amount of $160,795 were written down to their implied fair value of $153,922 as part of the Company’s annual impairment assessment on October 1, 2016. This resulted in an impairment charge of $6,873 , which was recorded to other operating expense, net, on the consolidated statements of operations.

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The following table presents the components of accumulated other comprehensive income (loss), net of tax, as of December 31, 2018 and 2017 : December 31, 2018 2017 Amortization and unrealized gains (losses) on pension and postretirement plans, net of tax of ($2,362) and ($4,761) $ (546 ) $ 7,412 Net changes in fair values of derivatives, net of tax of ($474) and ($584) 637 967 Foreign currency translation adjustments, net of tax of $5,154 and $790 (39,195 ) (4,068 ) Accumulated other comprehensive income (loss) $ (39,104 ) $ 4,311 The following table presents the tax effects of each component of other comprehensive income (loss) for the years ended December 31, 2018 , 2017 and 2016 : Years ended 2018 2017 2016 Pre-tax amount Tax benefit/ (expense) After-tax amount Pre-tax amount Tax benefit/ (expense) After-tax amount Pre-tax amount Tax benefit/ (expense) After-tax amount Defined benefit and other postretirement plans: Amortization and unrealized gains (losses) $ (10,357 ) $ 2,399 $ (7,958 ) $ (139 ) $ 38 $ (101 ) $ 11,664 $ (4,799 ) $ 6,865 Benefit plans, net (10,357 ) 2,399 (7,958 ) (139 ) 38 (101 ) 11,664 (4,799 ) 6,865 Net gain (loss) from hedging activities (441 ) 110 (331 ) (5,799 ) 2,209 (3,590 ) 7,350 (2,793 ) 4,557 Foreign currency translation (39,419 ) 4,364 (35,055 ) 66,438 (5,837 ) 60,601 (73,461 ) 6,627 (66,834 ) Other comprehensive income (loss) $ (50,217 ) $ 6,873 $ (43,344 ) $ 60,500 $ (3,590 ) $ 56,910 $ (54,447 ) $ (965 ) $ (55,412 ) The following table presents the change in accumulated other comprehensive income (loss), net of tax, by component for the years ended December 31, 2018 and 2017 : Defined benefit Net gain (loss) from hedging activities Foreign Total December 31, 2016 $ 7,513 $ 4,557 $ (65,781 ) $ (53,711 ) Other comprehensive income (loss) before reclassifications 6 (3,797) 61,713 57,922 Amounts reclassified from accumulated other comprehensive income (loss) (1) (107) 207 — 100 Net current period other comprehensive income (loss) (101) (3,590) 61,713 58,022 December 31, 2017 $ 7,412 $ 967 $ (4,068 ) $ 4,311 Other comprehensive loss before reclassifications (7,874) (257) (35,127) (43,258) Amounts reclassified from accumulated other comprehensive income (loss) (1) (84) (73) — (157) Net current period other comprehensive loss (7,958) (330) (35,127) (43,415) December 31, 2018 (546) 637 (39,195) (39,104) (1) See the following table for details about these reclassifications. Amounts in parentheses indicate credits to profit/loss.
Reclassification out of Accumulated Other Comprehensive Income	The following table presents the reclassifications out of accumulated other comprehensive income (loss) for the years ended December 31, 2018 and 2017 . Details about Accumulated Other Amount Reclassified from Accumulated Other Comprehensive Income (Loss) (a) Affected Line Item in the Years ended 2018 2017 Defined benefit and other postretirement plans: Amortization of prior service credit $ (112 ) $ (78 ) (b) Amortization of net (gain) loss 12 (54 ) (b) (100 ) (132 ) Total before tax 16 25 Tax expense (benefit) $ (84 ) $ (107 ) Net of tax Net (gain) loss from hedging activities: Interest rate caps $ 256 $ 40 Interest expense Natural gas swaps (353 ) 222 Cost of goods sold (97 ) 262 Total before tax 24 (55 ) Tax expense (benefit) $ (73 ) $ 207 Net of tax Total reclassifications for the period $ (157 ) $ 100 Net of tax (a) Amounts in parentheses indicate credits to profit/loss. (b) These accumulated other comprehensive income (loss) components are included in the computation of net periodic pension and other postretirement cost (see Note 20 to these consolidated financial statements for additional details).

Business Combination (Tables)

Business Combination (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Purchase Price Allocation	The following table sets forth the calculation and allocation of the purchase price to the net assets acquired of PQ Holdings with respect to the Business Combination, which was complete as of December 31, 2016. Total consideration, net of cash acquired $ 2,689,941 Recognized amounts of identifiable assets acquired and liabilities assumed: Receivables $ 161,110 Inventories 254,770 Prepaid and other current assets 19,295 Investments in affiliated companies 472,994 Property, plant and equipment 683,673 Other intangible assets 754,000 Other long-term assets 48,127 Fair value of assets acquired 2,393,969 Revolver, notes payable & current debt (2,441 ) Accounts payable (93,222 ) Accrued liabilities (98,621 ) Long-term debt (20,470 ) Deferred income taxes (327,296 ) Other long-term liabilities (113,936 ) Noncontrolling interest (6,569 ) Fair value of net assets acquired 1,731,414 Goodwill 958,527 $ 2,689,941 The following table sets forth the calculation and allocation of the purchase price to the identifiable net assets acquired with respect to the Acquisition, which was complete as of March 31, 2018: Provisional Purchase Adjustments Purchase Total consideration, net of cash acquired $ 41,572 $ — $ 41,572 Recognized amounts of identifiable assets acquired and liabilities assumed: Receivables $ 14,305 $ — $ 14,305 Inventories 7,645 1,603 9,248 Prepaid and other current assets 400 — 400 Property, plant and equipment 9,020 15,960 24,980 Other intangible assets — 5,753 5,753 Other long-term assets 129 15,921 16,050 Fair value of assets acquired 31,499 39,237 70,736 Current debt (6,420 ) — (6,420 ) Accounts payable (10,748 ) — (10,748 ) Long-term debt (10,189 ) — (10,189 ) Deferred income taxes — (4,426 ) (4,426 ) Other long-term liabilities (154 ) — (154 ) Fair value of net assets acquired 3,988 34,811 38,799 Goodwill 37,584 (34,811 ) 2,773 $ 41,572 $ — $ 41,572
Finite-Lived and Indefinite-Lived Intangible Assets Acquired as Part of Business Combination	The valuation of the intangible assets acquired and the related weighted-average amortization periods are as follows: Amount Weighted-Average Intangible assets subject to amortization: Trademarks $ 35,400 15.0 Technical know-how 189,300 20.0 Contracts 19,800 5.3 Customer relationships 268,700 10.6 In-process research and development 6,800 Total intangible assets subject to amortization 520,000 Trade names, not subject to amortization 151,100 Indefinite Trademarks, not subject to amortization 82,900 Indefinite Total $ 754,000 The valuation of the intangible assets acquired and the related weighted-average amortization periods are as follows: Amount Weighted-Average Intangible assets subject to amortization: Trademarks $ 1,767 11 Technical know-how 1,892 11 Total intangible assets subject to amortization 3,659 Trade names, not subject to amortization 2,094 Indefinite Total $ 5,753
Business Acquisition, Pro Forma Information	Year ended Pro forma sales $ 1,403,041 Pro forma net loss (76,994 ) Years ended 2017 2016 Pro forma sales $ 1,488,528 $ 1,105,479 Pro forma net income (loss) 58,774 (78,234 ) Pro forma net income (loss) attributable to PQ Group Holdings Inc. 57,814 (78,822 ) Pro forma basic income (loss) per share $ 0.52 $ (1.01 ) Pro forma diluted income (loss) per share $ 0.52 $ (1.01 )

Acquisition (Tables)

Acquisition (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Purchase Price Allocation	The following table sets forth the calculation and allocation of the purchase price to the net assets acquired of PQ Holdings with respect to the Business Combination, which was complete as of December 31, 2016. Total consideration, net of cash acquired $ 2,689,941 Recognized amounts of identifiable assets acquired and liabilities assumed: Receivables $ 161,110 Inventories 254,770 Prepaid and other current assets 19,295 Investments in affiliated companies 472,994 Property, plant and equipment 683,673 Other intangible assets 754,000 Other long-term assets 48,127 Fair value of assets acquired 2,393,969 Revolver, notes payable & current debt (2,441 ) Accounts payable (93,222 ) Accrued liabilities (98,621 ) Long-term debt (20,470 ) Deferred income taxes (327,296 ) Other long-term liabilities (113,936 ) Noncontrolling interest (6,569 ) Fair value of net assets acquired 1,731,414 Goodwill 958,527 $ 2,689,941 The following table sets forth the calculation and allocation of the purchase price to the identifiable net assets acquired with respect to the Acquisition, which was complete as of March 31, 2018: Provisional Purchase Adjustments Purchase Total consideration, net of cash acquired $ 41,572 $ — $ 41,572 Recognized amounts of identifiable assets acquired and liabilities assumed: Receivables $ 14,305 $ — $ 14,305 Inventories 7,645 1,603 9,248 Prepaid and other current assets 400 — 400 Property, plant and equipment 9,020 15,960 24,980 Other intangible assets — 5,753 5,753 Other long-term assets 129 15,921 16,050 Fair value of assets acquired 31,499 39,237 70,736 Current debt (6,420 ) — (6,420 ) Accounts payable (10,748 ) — (10,748 ) Long-term debt (10,189 ) — (10,189 ) Deferred income taxes — (4,426 ) (4,426 ) Other long-term liabilities (154 ) — (154 ) Fair value of net assets acquired 3,988 34,811 38,799 Goodwill 37,584 (34,811 ) 2,773 $ 41,572 $ — $ 41,572
Finite-Lived and Indefinite-Lived Intangible Assets Acquired as Part of Business Combination	The valuation of the intangible assets acquired and the related weighted-average amortization periods are as follows: Amount Weighted-Average Intangible assets subject to amortization: Trademarks $ 35,400 15.0 Technical know-how 189,300 20.0 Contracts 19,800 5.3 Customer relationships 268,700 10.6 In-process research and development 6,800 Total intangible assets subject to amortization 520,000 Trade names, not subject to amortization 151,100 Indefinite Trademarks, not subject to amortization 82,900 Indefinite Total $ 754,000 The valuation of the intangible assets acquired and the related weighted-average amortization periods are as follows: Amount Weighted-Average Intangible assets subject to amortization: Trademarks $ 1,767 11 Technical know-how 1,892 11 Total intangible assets subject to amortization 3,659 Trade names, not subject to amortization 2,094 Indefinite Total $ 5,753
Business Acquisition, Pro Forma Information	Year ended Pro forma sales $ 1,403,041 Pro forma net loss (76,994 ) Years ended 2017 2016 Pro forma sales $ 1,488,528 $ 1,105,479 Pro forma net income (loss) 58,774 (78,234 ) Pro forma net income (loss) attributable to PQ Group Holdings Inc. 57,814 (78,822 ) Pro forma basic income (loss) per share $ 0.52 $ (1.01 ) Pro forma diluted income (loss) per share $ 0.52 $ (1.01 )

Other Operating Expense, Net (T

Other Operating Expense, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Other Income and Expenses [Abstract]
Schedule of Other Nonoperating Income (Expense)	A summary of other operating expense, net is as follows: Years ended 2018 2017 2016 Amortization expense $ 35,025 $ 32,010 $ 25,263 Transaction and other related costs (1) 776 7,415 4,952 Restructuring and other related costs (Note 24) 6,208 8,490 12,630 Net loss on asset disposals 6,574 5,793 4,216 Intangible asset impairment charge (Note 14) — — 6,873 Management advisory fees (Note 26) — 3,777 3,584 Insurance recoveries (2) (5,480 ) — — Write-off of long-term supply contract obligation (Note 25) (20,612 ) — — Other, net 6,959 6,740 4,783 $ 29,450 $ 64,225 $ 62,301 (1) Transaction and other related costs for the years ended December 31, 2018 and 2017 primarily include transaction costs associated with the Company’s IPO, exclusive of the direct costs recorded in stockholders’ equity net of the proceeds from the offering (see Note 1 to these consolidated financial statements for further information) and the Acquisition (see Note 8 ). Transaction and other related costs for the year ended December 31, 2016 primarily include transaction costs directly attributable to the Business Combination (see Note 7 ) as well as other business development costs. (2) During the year ended December 31, 2018 , the Company recognized $6,450 of insurance recoveries in its consolidated statement of operations related to the Company’s claim for losses sustained during Hurricane Harvey in August 2017. For the year ended December 31, 2018 , $5,480 was recorded as a gain in other operating expense, net, as reimbursement of expenses, $207 was recorded as a gain in net loss on asset disposals within other operating expense, net, for the Company’s previously recognized property losses, and $813 represented recoveries in excess of the Company’s property losses which was recorded as a non-operating gain in other expense, net, in the Company’s consolidated statement of operations.

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Schedule of Inventory, Current	Inventories are classified and valued as follows: December 31, 2018 2017 Finished products and work in process $ 206,188 $ 199,919 Raw materials 58,560 62,469 $ 264,748 $ 262,388 Valued at lower of cost or market: LIFO basis $ 160,863 $ 162,315 Valued at lower of cost and net realizable value: FIFO or average cost basis 103,885 100,073 $ 264,748 $ 262,388

Investments in Affiliated Com_2

Investments in Affiliated Companies (Tables)	12 Months Ended
	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments	Affiliated companies accounted for on the equity method as of December 31, 2018 are as follows: Company Country Percent PQ Silicates Ltd. Taiwan 50% Zeolyst International USA 50% Zeolyst C.V. Netherlands 50% Quaker Holdings South Africa 49% Asociacion para el Estudio de las Tecnologias de Equipamiento de Carreteras, S.A. (“Aetec”) Spain 20% Following is summarized information of the combined investments (1) : December 31, 2018 2017 Current assets $ 215,416 $ 213,815 Noncurrent assets 248,288 235,440 Current liabilities 40,536 37,018 Noncurrent liabilities 56 1,417 Years ended December 31, 2018 2017 2016 Sales $ 352,599 $ 317,197 $ 206,072 Gross profit 126,945 132,812 91,761 Operating income 88,508 91,224 67,098 Net income 88,622 94,740 67,332 (1) Summarized information of the combined investments is presented at 100%; the Company’s share of the net assets and net income of affiliates is calculated based on the percent ownership specified in the table above. The following table summarizes the activity related to the Company’s investments in affiliated companies balance on the consolidated balance sheets: Years ended 2018 2017 Balance at beginning of period $ 469,276 $ 459,406 Acquisition — 119 Investments in affiliated companies 5,000 9,000 Equity in net income of affiliated companies 44,245 47,371 Charges related to purchase accounting fair value adjustments (6,634 ) (8,599 ) Dividends received (40,890 ) (44,071 ) Foreign currency translation adjustments (2,786 ) 6,050 Balance at end of period $ 468,211 $ 469,276

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	A summary of property, plant and equipment, at cost, and related accumulated depreciation is as follows: December 31, 2018 2017 Land $ 190,772 $ 191,006 Buildings 212,284 200,054 Machinery and equipment 1,125,117 1,005,025 Construction in progress 102,185 145,414 1,630,358 1,541,499 Less: accumulated depreciation (421,379 ) (311,115 ) $ 1,208,979 $ 1,230,384

Reportable Segments (Tables)

Reportable Segments (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Reconciliation of Revenue from Reportable Segments to Consolidated	Summarized financial information for the Company’s reportable segments and product groups is shown in the following table: Years ended 2018 2017 2016 Sales: Silica Catalysts $ 72,099 $ 75,333 $ 53,029 Refining Services 455,562 398,342 373,718 Environmental Catalysts & Services (1) 527,661 473,675 426,747 Performance Chemicals $ 717,335 $ 687,645 $ 437,523 Performance Materials 378,279 324,225 206,522 Eliminations (11,798 ) (10,021 ) (5,094 ) Performance Materials & Chemicals 1,083,816 1,001,849 638,951 Inter-segment sales eliminations (2) (3,323 ) (3,423 ) (1,521 ) Total $ 1,608,154 $ 1,472,101 $ 1,064,177 Segment Adjusted EBITDA: (3) Environmental Catalysts & Services (4) $ 257,566 $ 243,587 $ 196,825 Performance Materials & Chemicals 243,357 240,128 158,679 Total Segment Adjusted EBITDA (5) $ 500,923 $ 483,715 $ 355,504 (1) Excludes the Company’s proportionate share of sales from the Zeolyst International and Zeolyst C.V. joint ventures (collectively, the “Zeolyst Joint Venture”) accounted for using the equity method (see Note 11 to these consolidated consolidated financial statements for further information). The proportionate share of sales is $156,687 , $143,774 and $94,516 for the years ended December 31, 2018 , 2017 and 2016 , respectively. (2) The Company eliminates intersegment sales when reconciling to the Company’s consolidated statements of operations. (3) The Company defines Adjusted EBITDA as EBITDA adjusted for certain items as noted in the reconciliation below. Management evaluates the performance of its segments and allocates resources based on several factors, of which the primary measure is Adjusted EBITDA. Adjusted EBITDA should not be considered as an alternative to net income as an indicator of the Company’s operating performance. Adjusted EBITDA as defined by the Company may not be comparable with EBITDA or Adjusted EBITDA as defined by other companies. (4) The Adjusted EBITDA from the Zeolyst Joint Venture included in the Environmental Catalysts and Services segment is $56,663 for the year ended December 31, 2018 , which includes $42,854 of equity in net income plus $6,634 of amortization of investment in affiliate step-up plus $12,592 of joint venture depreciation, amortization and interest. The Adjusted EBITDA from the Zeolyst Joint Venture included in the Environmental Catalysts and Services segment is $58,156 for the year ended December 31, 2017 , which includes $46,252 of equity in net income plus $8,600 of amortization of investment in affiliate step-up plus $11,070 of joint venture depreciation, amortization and interest. The Adjusted EBITDA from the Zeolyst Joint Venture included in the Environmental Catalysts and Services segment is $39,903 for the year ended December 31, 2016 , which includes $3,313 of equity in net loss plus $36,296 of amortization of investment in affiliate step-up plus $6,920 of joint venture depreciation, amortization and interest. (5) Total Segment Adjusted EBITDA differs from the Company’s consolidated Adjusted EBITDA due to unallocated corporate expenses.
Reconciliation of Net Loss to Segment Adjusted EBITDA	A reconciliation of net income (loss) attributable to PQ Group Holdings to Segment Adjusted EBITDA is as follows: Years ended 2018 2017 2016 Reconciliation of net income attributable to PQ Group Holdings Inc. to Segment Adjusted EBITDA Net income (loss) attributable to PQ Group Holdings Inc. $ 58,300 $ 57,603 $ (79,746 ) Provision for (benefit from) income taxes 28,995 (119,197 ) 10,041 Interest expense, net 113,723 179,044 140,315 Depreciation and amortization 185,234 177,140 128,288 Segment EBITDA 386,252 294,590 198,898 Unallocated corporate expenses 36,970 30,422 23,971 Joint venture depreciation, amortization and interest 12,592 11,070 6,920 Amortization of investment in affiliate step-up 6,634 8,600 36,296 Amortization of inventory step-up 1,603 871 29,086 Impairment of fixed assets, intangibles and goodwill — — 6,873 Debt extinguishment costs 7,751 61,886 13,782 Net loss on asset disposals 6,574 5,793 4,216 Foreign currency exchange loss (gain) 13,810 25,786 (3,558 ) LIFO expense 8,366 3,708 1,310 Management advisory fees — 3,777 3,583 Transaction and other related costs 893 7,425 4,664 Equity-based compensation 19,464 8,799 7,042 Restructuring, integration and business optimization expenses 14,019 13,174 16,258 Defined benefit pension plan cost (796 ) 2,940 1,375 Gain on contract termination (1) (20,612 ) — — Other 7,403 4,874 4,788 Segment Adjusted EBITDA $ 500,923 $ 483,715 $ 355,504 (1) Includes the non-cash write-off of a long-term supply contract obligation (see Note 25 ), which was recorded as a reduction in other operating expense, net in the consolidated statement of operations for the year ended December 31, 2018 .
Reconciliation of Assets from Segment to Consolidated	Capital expenditures for the Company’s reportable segments are shown in the following table: Years ended 2018 2017 2016 Capital expenditures: Environmental Catalysts & Services (1) $ 55,007 $ 53,145 $ 57,803 Performance Materials & Chemicals 75,476 84,783 71,293 Corporate (2) 1,205 2,554 (7,675 ) Capital expenditures per the consolidated statements of cash flows $ 131,688 $ 140,482 $ 121,421 (1) Excludes the Company’s proportionate share of capital expenditures from the Zeolyst Joint Venture. (2) Includes corporate capital expenditures, the cash impact from changes in capital expenditures in accounts payable and capitalized interest.
Revenue from External Customers by Geographic Areas	Sales and long-lived assets by geographic area are presented in the following tables. Sales are attributed to countries based upon location of products shipped. Years ended 2018 2017 2016 Sales (1) : United States $ 963,722 $ 874,764 $ 705,348 Netherlands 127,803 118,567 79,821 United Kingdom 119,586 116,410 67,494 Other foreign countries 397,043 362,360 211,514 Total $ 1,608,154 $ 1,472,101 $ 1,064,177 (1) Except for the United States, no sales in an individual country exceeded 10% of the Company’s total sales.
Long-lived Assets by Geographic Areas	December 31, 2018 2017 Long-lived assets (1) : United States $ 865,799 $ 891,861 Netherlands 52,461 52,882 United Kingdom 90,095 90,536 Other foreign countries 200,624 195,105 Total $ 1,208,979 $ 1,230,384 (1) Long-lived assets include property, plant and equipment, net.

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The changes in the carrying amount of goodwill for the years ended December 31, 2018 and 2017 is summarized as follows: Environmental Performance Total Balance as of December 31, 2016 $ 388,923 $ 852,506 $ 1,241,429 Goodwill recognized — 37,584 37,584 Foreign exchange impact 2,410 24,533 26,943 Balance as of December 31, 2017 $ 391,333 $ 914,623 $ 1,305,956 Goodwill recognized — 649 649 Goodwill adjustments (1) — (34,811 ) (34,811 ) Foreign exchange impact and other (1,682 ) (15,183 ) (16,865 ) Balance as of December 31, 2018 $ 389,651 $ 865,278 $ 1,254,929 (1) Represents the measurement period adjustments on the net assets acquired as part of the Acquisition (see Note 8 to these consolidated financial statements for further information regarding the Acquisition).
Schedule of Finite-Lived Intangible Assets	Gross carrying amounts and accumulated amortization for intangible assets other than goodwill are as follows: December 31, 2018 December 31, 2017 Gross Amount Accumulated Net Gross Amount Accumulated Net Balance Technical know-how $ 211,067 $ (32,112 ) $ 178,955 $ 212,599 $ (21,138 ) $ 191,461 Customer relationships 361,150 (95,399 ) 265,751 366,021 (63,860 ) 302,161 Contracts 19,800 (13,139 ) 6,661 19,800 (9,205 ) 10,595 Trademarks 36,657 (6,451 ) 30,206 35,202 (3,911 ) 31,291 Permits 9,100 (7,432 ) 1,668 9,100 (5,612 ) 3,488 Total definite-lived intangible assets 637,774 (154,533 ) 483,241 642,722 (103,726 ) 538,996 Indefinite-lived trade names 157,813 — 157,813 158,059 — 158,059 Indefinite-lived trademarks 80,582 — 80,582 82,289 — 82,289 In-process research and development 6,800 — 6,800 6,800 — 6,800 Total intangible assets $ 882,969 $ (154,533 ) $ 728,436 $ 889,870 $ (103,726 ) $ 786,144
Schedule of Indefinite-Lived Intangible Assets	Gross carrying amounts and accumulated amortization for intangible assets other than goodwill are as follows: December 31, 2018 December 31, 2017 Gross Amount Accumulated Net Gross Amount Accumulated Net Balance Technical know-how $ 211,067 $ (32,112 ) $ 178,955 $ 212,599 $ (21,138 ) $ 191,461 Customer relationships 361,150 (95,399 ) 265,751 366,021 (63,860 ) 302,161 Contracts 19,800 (13,139 ) 6,661 19,800 (9,205 ) 10,595 Trademarks 36,657 (6,451 ) 30,206 35,202 (3,911 ) 31,291 Permits 9,100 (7,432 ) 1,668 9,100 (5,612 ) 3,488 Total definite-lived intangible assets 637,774 (154,533 ) 483,241 642,722 (103,726 ) 538,996 Indefinite-lived trade names 157,813 — 157,813 158,059 — 158,059 Indefinite-lived trademarks 80,582 — 80,582 82,289 — 82,289 In-process research and development 6,800 — 6,800 6,800 — 6,800 Total intangible assets $ 882,969 $ (154,533 ) $ 728,436 $ 889,870 $ (103,726 ) $ 786,144
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Estimated future aggregate amortization expense of intangible assets is as follows: Year Amount 2019 $ 50,652 2020 47,101 2021 46,159 2022 46,092 2023 42,175 Thereafter 251,062 Total estimated future aggregate amortization expense $ 483,241

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	The following table summarizes the components of accrued liabilities as follows: December 31, 2018 2017 Compensation and bonus $ 52,296 $ 49,988 Interest 21,933 15,936 Property tax 3,018 1,622 Environmental reserves (see Note 23) 4,693 5,790 Supply contract obligation (see Note 25) — 1,638 Income taxes 2,123 1,166 Commissions and rebates 1,798 1,820 Pension, postretirement and supplemental retirement plans (see Note 20) 2,439 2,192 Other 11,709 13,765 $ 100,009 $ 93,917

Long-term Debt (Tables)

Long-term Debt (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments	The summary of long-term debt is as follows: December 31, 2018 2017 Term Loan Facility (U.S. dollar denominated) $ — $ 916,153 Term Loan Facility (Euro denominated) — 335,808 New Term Loan Facility 1,157,498 — 6.75% Senior Secured Notes due 2022 625,000 625,000 5.75% Senior Unsecured Notes due 2025 300,000 300,000 ABL Facility — 25,000 Other 65,925 68,318 Total debt 2,148,423 2,270,279 Original issue discount (18,584 ) (18,390 ) Deferred financing costs (15,882 ) (21,403 ) Total debt, net of original issue discount and deferred financing costs 2,113,957 2,230,486 Less: current portion (7,237 ) (45,166 ) Total long-term debt, excluding current portion $ 2,106,720 $ 2,185,320
Debt Instrument Redemption	On or after December 15, 2020, the 5.75% Senior Unsecured Notes are redeemable, in whole or in part, at the redemption prices (expressed as percentages of principal amount of the 5.75% Senior Unsecured Notes to be redeemed) set forth below, plus accrued and unpaid interest, if any, to, but not including, the redemption date, if redeemed on or after any of the dates below until the subsequent date below: Year Percentage December 15, 2020 102.875% December 15, 2021 101.438% December 15, 2022 and thereafter 100.000% The 6.75% Senior Secured Notes are redeemable, in whole or in part, at the redemption prices (expressed as percentages of principal amount of the 6.75% Senior Secured Notes to be redeemed) set forth below, plus accrued and unpaid interest, if any, to, but not including, the redemption date, if redeemed on or after any of the dates below until the subsequent date below: Year Percentage May 15, 2019 103.375% May 15, 2020 101.688% May 15, 2021 and thereafter 100.000%
Fiscal Year Maturity Schedule	The aggregate long-term debt maturities are: Year Amount 2019 $ 7,237 2020 1,718 2021 1,717 2022 628,433 2023 3,689 Thereafter 1,505,629 $ 2,148,423

Other Long-term Liabilities (Ta

Other Long-term Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
Other Long-term Liabilities	The following table summarizes the components of other long-term liabilities as follows: December 31, 2018 2017 Pension benefits $ 75,430 $ 69,914 Supply contract (see Note 25) — 20,612 Other postretirement benefits 3,233 4,051 Supplemental retirement plans 10,763 11,667 Reserve for uncertain tax positions 3,176 4,244 Asset retirement obligation 4,224 4,094 Other 7,999 5,889 $ 104,825 $ 120,471

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair Value of Derivatives Held	The fair values of derivative instruments held as of December 31, 2018 and 2017 are shown below: December 31, Balance sheet location 2018 2017 Derivative assets: Derivatives designated as cash flow hedges: Natural gas swaps Prepaid and other current assets $ 21 $ — Interest rate caps Prepaid and other current assets 1,358 44 Interest rate caps Other long-term assets 546 999 1,925 1,043 Derivatives designed as net investment hedges: Cross currency swaps Prepaid and other current assets 5,499 — Cross currency swaps Other long-term assets 13,344 — 18,843 — Total derivative assets $ 20,768 $ 1,043 Derivative liabilities: Derivatives designated as cash flow hedges: Natural gas swaps Accrued liabilities $ 36 $ 318 Natural gas swaps Other long-term liabilities 148 130 Interest rate caps Other long-term liabilities 1,842 — Total derivative liabilities $ 2,026 $ 448
Effect of Derivative Instruments Designated as Hedges on Other Comprehensive Income	The following table shows the effect of the Company’s derivative instruments designated as hedges on accumulated other comprehensive income (loss) (“AOCI”) and the statements of operations for the years ended December 31, 2018 , 2017 and 2016 : Years ended December 31, 2018 2017 2016 Location of gain (loss) reclassified from AOCI into income Amount of gain (loss) recognized in OCI on derivatives Amount of gain (loss) reclassified from AOCI into income Amount of gain (loss) recognized in OCI on derivatives Amount of gain (loss) reclassified from AOCI into income Amount of gain (loss) recognized in OCI on derivatives Amount of gain (loss) reclassified from AOCI into income Interest rate caps Interest (expense) income $ (981 ) $ (256 ) $ (4,760 ) $ (40 ) $ 4,250 $ — Natural gas swaps Cost of goods sold $ 637 $ 353 $ (1,300 ) $ (222 ) $ (802 ) $ (1,433 ) $ (344 ) $ 97 $ (6,060 ) $ (262 ) $ 3,448 $ (1,433 )
Schedule of Effect of Cash Flow Hedging Instruments on the Statement of Operations	The following table shows the effect of the Company’s cash flow hedge accounting on the consolidated statements of operations for the years ended December 31, 2018 , 2017 and 2016 : Location and amount of gain (loss) recognized in income on cash flow hedging relationships Years ended December 31, 2018 2017 2016 Cost of goods sold Interest (expense) income Cost of goods sold Interest (expense) income Cost of goods sold Interest (expense) income Total amounts of income and expense line items presented in the statement of operations in which the effects of cash flow hedges are recorded $ (1,226,520 ) $ (113,723 ) $ (1,095,265 ) $ (179,044 ) $ (810,085 ) $ (140,315 ) The effects of cash flow hedging: Gain (loss) on cash flow hedging relationships: Interest contracts: Amount of gain (loss) reclassified from AOCI into income — (256 ) — (40 ) — — Commodity contracts: Amount of gain (loss) reclassified from AOCI into income 353 — (222 ) — (1,433 ) —
Schedule of Net Investment Hedges in Accumulated Other Comprehensive Income (Loss)	The following table shows the effect of the Company’s net investment hedges on AOCI and the consolidated statements of operations for the years ended December 31, 2018 , 2017 and 2016 : Amount of gain (loss) recognized in OCI on derivative Location of (gain) loss reclassified from AOCI into income Amount of (gain) loss reclassified from AOCI into income Location of gain (loss) recognized in income on derivative (amount excluded from effectiveness testing) Amount of gain (loss) recognized in income on derivative (amount excluded from effectiveness testing) Years ended December 31, Years ended December 31, Years ended December 31, 2018 2017 2016 2018 2017 2016 2018 2017 2016 Cross currency swaps $ 18,843 $ — $ — (Gain) loss on sale of subsidiary $ — $ — $ — Interest (expense) income $ 7,898 $ — $ —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	Income (loss) before income taxes and noncontrolling interest within or outside the United States are shown below: Years ended 2018 2017 2016 Domestic $ 3,935 $ (137,147 ) $ (84,094 ) Foreign 84,681 76,513 14,977 Total $ 88,616 $ (60,634 ) $ (69,117 )
Schedule of Components of Income Tax Expense (Benefit)	The provision (benefit) for income taxes as shown in the accompanying consolidated statements of operations consists of the following: Years ended 2018 2017 2016 Current: Federal $ — $ — $ — State 2,470 806 91 Foreign 23,080 20,209 10,088 25,550 21,015 10,179 Deferred: Federal 12,854 (135,970 ) 8,654 State (784 ) (1,817 ) 292 Foreign (8,625 ) (2,425 ) (9,084 ) 3,445 (140,212 ) (138 ) Provision (benefit) for income taxes $ 28,995 $ (119,197 ) $ 10,041
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of income tax expense (benefit) at the U.S. federal statutory income tax rate to actual income tax expense is as follows: Years ended 2018 2017 2016 Tax at statutory rate $ 18,610 $ (21,222 ) $ (24,191 ) State income taxes, net of federal income tax benefit 1,203 (7,754 ) (4,110 ) Repatriation of non-US earnings 14,187 (24,912 ) 4,576 Change in tax status-Eco Services-Passthrough to C-Corporation — — 33,891 Changes in uncertain tax positions (996 ) 974 (2,383 ) Change in valuation allowances 5,075 6,771 2,577 Rate changes (4,016 ) (63,319 ) — Change in state effective rates 691 (340 ) (290 ) Foreign withholding taxes 1,828 978 1,505 Foreign tax rate differential 2,191 (13,634 ) (3,040 ) Non-deductible transaction costs 84 1,679 667 Permanent difference created by foreign exchange gain or loss (7,550 ) 3,503 1,686 Research and development tax credits (1,173 ) — — Other, net (1,139 ) (1,921 ) (847 ) Provision (benefit) for income taxes $ 28,995 $ (119,197 ) $ 10,041
Schedule of Deferred Tax Assets and Liabilities	Deferred tax assets (liabilities) are comprised of the following: December 31, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 116,607 $ 144,267 Section 163j interest disallowance carryforward 13,387 — Pension 16,397 16,255 Post retirement health 1,385 561 Transaction costs 708 1,183 Natural gas contracts and interest rate swaps 335 225 Unrealized translation losses 3,737 5,065 US research and development credits 1,173 — Other 38,855 38,290 Valuation allowance (48,711 ) (64,945 ) $ 143,873 $ 140,901 Deferred tax liabilities: Depreciation $ (92,911 ) $ (86,532 ) Undistributed earnings of non-US subsidiaries (6,648 ) (8,334 ) Inventory (10,432 ) (11,324 ) Intangible assets (174,327 ) (184,937 ) Cross currency swaps (4,654 ) — Other (32,230 ) (36,810 ) $ (321,202 ) $ (327,937 ) Net deferred tax liabilities $ (177,329 ) $ (187,036 )
Summary of Valuation Allowance	The following are changes in the deferred tax valuation allowance during the years ended December 31, 2018 and 2017 : Years ended 2018 2017 Beginning Balance $ 64,945 $ 38,271 Additions 5,314 34,863 Reductions (21,548 ) (8,189 ) Ending Balance $ 48,711 $ 64,945
Schedule of Unrecognized Tax Benefits Roll Forward	The following table summarizes the activity related to the Company’s gross unrecognized tax benefits: Years ended 2018 2017 Balance at beginning of period $ 11,431 $ 16,128 Increases related to prior year tax positions — 68 Decreases related to prior year tax positions (1,538 ) (5,508 ) Increases related to current year tax positions 282 743 Balance at end of period $ 10,175 $ 11,431
Open Tax Years	The following describes the open tax years, by major tax jurisdiction, as of December 31, 2018 : Jurisdiction Period United States-Federal 2007-Present United States-State 2007-Present Canada (1) 2010-Present Germany 2015-Present Netherlands 2012-Present Mexico 2014-Present United Kingdom 2012-Present Brazil 2014-Present (1) Includes federal as well as local jurisdictions
Schedule of Tax Payments	Cash payments for income taxes, net of refunds, are as follows: Years ended 2018 2017 2016 Domestic $ 2,160 $ 1,647 $ 373 Foreign 21,682 27,552 16,608 $ 23,842 $ 29,199 $ 16,981

Benefit Plans (Tables)

Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2018
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	The following tables summarize changes in the benefit obligation, plan assets and funded status of the Company’s significant defined benefit pension plans as well as the components of net periodic benefit cost, including key assumptions: U.S. Foreign December 31, December 31, 2018 2017 2018 2017 Change in benefit obligation: Benefit obligation at beginning of period $ 261,102 $ 247,418 $ 119,710 $ 106,025 Service cost 1,019 1,219 3,566 3,686 Interest cost 9,599 10,115 3,340 3,271 Participant contributions — — 570 493 Plan amendments — — 179 — Plan curtailments (952 ) — (340 ) — Plan settlements — (2,264 ) (1,071 ) — Benefits paid (11,453 ) (9,591 ) (2,569 ) (2,967 ) Expenses paid — — (363 ) (319 ) Net transfer in — — 1,535 — Actuarial (gains) losses (13,004 ) 14,205 (5,432 ) (2,169 ) Translation adjustment — — (7,022 ) 11,690 Benefit obligation at end of the period $ 246,311 $ 261,102 $ 112,103 $ 119,710 Change in plan assets: Fair value of plan assets at beginning of period $ 218,374 $ 198,915 $ 96,518 $ 86,145 Actual return on plan assets (12,854 ) 27,554 (540 ) 217 Employer contributions 1,688 3,760 4,249 3,781 Employee contributions — — 570 493 Plan settlements — (2,264 ) (1,071 ) — Benefits paid (11,453 ) (9,591 ) (2,569 ) (2,967 ) Expenses paid — — (363 ) (319 ) Acquisitions — — 1,013 — Translation adjustment — — (6,020 ) 9,168 Fair value of plan assets at end of the period $ 195,755 $ 218,374 $ 91,787 $ 96,518 Funded status of the plans (underfunded) $ (50,556 ) $ (42,728 ) $ (20,316 ) $ (23,192 )
Schedule of Amounts Recognized in Balance Sheet	Amounts recognized in the consolidated balance sheets consist of: U.S. Foreign December 31, December 31, 2018 2017 2018 2017 Noncurrent asset $ — $ — $ 4,670 $ 3,503 Current liability — — (748 ) (673 ) Noncurrent liability (50,556 ) (42,728 ) (24,238 ) (26,022 ) Accumulated other comprehensive income (loss) 1,218 10,499 (1,829 ) (2,871 ) Net amount recognized $ (49,338 ) $ (32,229 ) $ (22,145 ) $ (26,063 )
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	Amounts recognized in accumulated other comprehensive income (loss) consist of: U.S. Foreign December 31, December 31, 2018 2017 2018 2017 Prior service cost $ — $ — $ (170 ) $ — Net gain (loss) 1,618 13,943 (2,133 ) (3,923 ) Gross amount recognized 1,618 13,943 (2,303 ) (3,923 ) Deferred income taxes (400 ) (3,444 ) 474 1,052 Net amount recognized $ 1,218 $ 10,499 $ (1,829 ) $ (2,871 )
Components of Net Periodic Expense	Components of net periodic benefit cost consist of: U.S. Foreign Years ended Years ended 2018 2017 2016 2018 2017 2016 Service cost $ 1,019 $ 1,219 $ 2,130 $ 3,566 $ 3,686 $ 2,106 Interest cost 9,599 10,115 7,680 3,340 3,271 2,224 Expected return on plan assets (12,851 ) (12,277 ) (9,293 ) (3,311 ) (3,208 ) (2,038 ) Amortization of net (gain) loss — — — 49 (9 ) (10 ) Curtailment gain recognized (576 ) — (1,311 ) (340 ) — (517 ) Settlement (gain) loss recognized — (48 ) 152 (11 ) — — Net periodic expense (benefit) $ (2,809 ) $ (991 ) $ (642 ) $ 3,293 $ 3,740 $ 1,765
Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets	The following table presents selected information about the Company’s pension plans with accumulated benefit obligations in excess of plan assets: U.S. Foreign December 31, December 31, 2018 2017 2018 2017 Projected benefit obligation $ 246,311 $ 261,102 $ 82,656 67,750 Accumulated benefit obligation 244,580 257,882 78,862 64,526 Fair value of plan assets 195,755 218,374 57,670 42,632
Schedule of Assumptions Used	Significant weighted average assumptions used in determining the pension obligations include the following: U.S. Foreign December 31, December 31, 2018 2017 2018 2017 Discount rate 4.32 % 3.74 % 3.01 % 2.91 % Rate of compensation increase (1) 3.00 % 3.00 % 2.44 % 2.57 % Significant weighted average assumptions used in determining net periodic benefit cost include the following: U.S. Foreign Years ended Years ended 2018 2017 2016 2018 2017 2016 Discount rate 3.74 % 4.24 % 4.02 % 2.91 % 2.99 % 5.16 % Rate of compensation increase (1) 3.00 % 3.00 % 3.10 % 2.57 % 2.97 % 3.95 % Expected return on assets 6.00 % 6.37 % 6.34 % 3.52 % 3.58 % 5.62 %
Schedule of Allocation of Plan Assets	The following tables set forth by level, within the fair value hierarchy, plan assets at fair value: December 31, 2018 Total Level 1 Level 2 Level 3 Cash and cash equivalents (1) $ 57,000 $ 56,925 $ 75 $ — Equity securities: U.S. investment funds 35,103 35,103 — — International investment funds 44,508 24,040 20,468 — Fixed income securities: Government securities 10,121 — 10,121 — Corporate bonds 77,229 72,216 5,013 — Investment fund bonds 25,152 7,665 17,487 — Other: Insurance contracts 38,429 — 33,408 5,021 Total $ 287,542 $ 195,949 $ 86,572 $ 5,021 December 31, 2017 Total Level 1 Level 2 Level 3 Cash and cash equivalents $ 1,072 $ 934 $ 138 $ — Equity securities: U.S. investment funds 56,309 43,625 12,684 — International investment funds 70,308 28,827 41,481 — Fixed income securities: Government securities 11,433 — 11,433 — Corporate bonds 82,585 77,685 4,900 — Investment fund bonds 54,263 7,719 46,544 — Other: Insurance contracts 38,922 — 34,772 4,150 Total $ 314,892 $ 158,790 $ 151,952 $ 4,150 (1) Level 1 balance includes $55,905 of cash and cash equivalents held by two of the Company’s U.S. defined benefit pension plans. The investments in equity securities and fixed income securities previously held by these plans were liquidated into cash and cash equivalents in December 2018 in preparation for a transfer of plan assets to a new custodian. This transfer was completed in January 2019.
Defined Benefit Plan Level 3 Assets	The changes in the Level 3 pension plan assets are as follows for the years ended December 31: Insurance Contracts 2018 2017 Beginning balance $ 4,150 $ 3,286 Actual return on plan assets 10 (41 ) Benefits paid (385 ) (48 ) Contributions 461 466 Exchange rate changes and other 785 487 Ending balance $ 5,021 $ 4,150
Schedule of Expected Benefit Payments	The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid: Year U.S. Foreign 2019 $ 15,369 $ 3,115 2020 16,253 2,769 2021 16,966 2,952 2022 15,894 3,366 2023 15,823 3,630 Years 2024-2028 78,304 23,111
Supplemental Retirement Plans
Defined Benefit Plan Disclosure
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	The following tables summarize changes in the benefit obligation, plan assets and funded status of the Company’s defined benefit supplementary retirement plans, as well as the components of net periodic benefit cost, including key assumptions: December 31, 2018 2017 Change in benefit obligation: Benefit obligation at beginning of period $ 12,781 $ 13,225 Interest cost 450 489 Benefits paid (1,070 ) (1,179 ) Actuarial (gains) losses (293 ) 246 Benefit obligation at end of period $ 11,868 $ 12,781 Change in plan assets: Fair value of plan assets at beginning of period $ — $ — Employer contributions 1,070 1,179 Benefits paid (1,070 ) (1,179 ) Fair value of plan assets at end of period $ — $ — Funded status of the plans (underfunded) $ (11,868 ) $ (12,781 )
Schedule of Amounts Recognized in Balance Sheet	Amounts recognized in the consolidated balance sheets consist of: December 31, 2018 2017 Current liability $ (1,105 ) $ (1,115 ) Noncurrent liability (10,763 ) (11,667 ) Accumulated other comprehensive income 795 573 Net amount recognized $ (11,073 ) $ (12,209 )
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	Amounts recognized in accumulated other comprehensive income consist of: December 31, 2018 2017 Net gain $ 1,055 $ 761 Gross amount recognized 1,055 761 Deferred income taxes (260 ) (188 ) Net amount recognized $ 795 $ 573
Components of Net Periodic Expense	Components of net periodic benefit cost consist of: Years ended 2018 2017 2016 Interest cost $ 450 $ 489 $ 328 Net periodic expense $ 450 $ 489 $ 328
Schedule of Expected Benefit Payments	The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid: Year Amount 2019 $ 1,105 2020 1,076 2021 1,045 2022 1,009 2023 970 Years 2024-2028 4,276
Other Postretirement Benefits Plans
Defined Benefit Plan Disclosure
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	The following tables summarize changes in the benefit obligation, plan assets and funded status of the Company’s other postretirement benefit plans as well as the components of net periodic benefit cost, including key assumptions: December 31, 2018 2017 Change in benefit obligation: Benefit obligation at beginning of period $ 4,612 $ 4,620 Service cost 16 21 Interest cost 150 174 Employee contributions 251 251 Plan amendments (271 ) — Benefits paid (1,061 ) (923 ) Medical subsidies received 74 — Premiums paid (66 ) (3 ) Actuarial (gains) losses 172 418 Translation adjustment (63 ) 54 Benefit obligation at end of period $ 3,814 $ 4,612 Change in plan assets: Fair value of plan assets at beginning of period — — Employer contributions 802 675 Employee contributions 251 251 Benefits paid (1,061 ) (923 ) Medical subsidies received 74 — Premiums paid (66 ) (3 ) Fair value of plan assets at end of period $ — $ — Funded status of the plans (underfunded) $ (3,814 ) $ (4,612 )
Schedule of Amounts Recognized in Balance Sheet	Amounts recognized in the consolidated balance sheets consist of: December 31, 2018 2017 Current liability $ (581 ) $ (561 ) Noncurrent liability (3,233 ) (4,051 ) Accumulated other comprehensive income 830 885 Net amount recognized $ (2,984 ) $ (3,727 )
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	Amounts recognized in accumulated other comprehensive income consist of: December 31, 2018 2017 Prior service credit $ 525 $ 366 Net gain 500 719 Gross amount recognized 1,025 1,085 Deferred income taxes (195 ) (200 ) Net amount recognized $ 830 $ 885
Components of Net Periodic Expense	Components of net periodic benefit cost consist of: Years ended 2018 2017 2016 Service cost $ 16 $ 21 $ 37 Interest cost 150 174 151 Amortization of prior service credit (112 ) (78 ) — Amortization of net gain (26 ) (45 ) (17 ) Net periodic expense $ 28 $ 72 $ 171
Schedule of Assumptions Used	: December 31, 2018 2017 Immediate trend rate 6.59% 6.84% Ultimate trend rate 4.50% 4.50% Year that the rate reaches ultimate trend rate 2035 2035
Schedule of Expected Benefit Payments	The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid: Year Amount 2019 $ 581 2020 514 2021 388 2022 313 2023 272 Years 2024-2028 915
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates	A 1% change in the assumed health care cost trend would have increased (decreased) the accumulated postretirement benefit obligation as of December 31, 2018 and the periodic postretirement benefit cost for the year then ended as follows: 1% Increase 1% Decrease Accumulated postretirement benefit obligation $ 157 $ (138 ) Periodic postretirement benefit cost 6 (5 )

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of from Basic to Diluted Weighted Average Number of Shares Outstanding	The reconciliation from basic to diluted weighted average shares outstanding is as follows: Years ended 2018 2017 2016 Weighted average shares outstanding – Basic 133,380,567 111,299,670 78,016,005 Dilutive effect of unvested common shares and restricted stock units with service conditions and assumed stock option exercises and conversions 1,304,364 369,367 — Weighted average shares outstanding – Diluted 134,684,931 111,669,037 78,016,005
Schedule of Earnings Per Share, Basic and Diluted	Basic and diluted earnings per share are calculated as follows: Years ended 2018 2017 2016 Numerator: Net income (loss) attributable to PQ Group Holdings Inc. $ 58,300 $ 57,603 $ (79,746 ) Denominator: Weighted average shares outstanding – Basic 133,380,567 111,299,670 78,016,005 Weighted average shares outstanding – Diluted 134,684,931 111,669,037 78,016,005 Net income (loss) per share: Basic income (loss) per share $ 0.44 $ 0.52 $ (1.02 ) Diluted income (loss) per share $ 0.43 $ 0.52 $ (1.02 )
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The table below presents the details of the Company’s equity-based awards outstanding at the end of each respective year that were excluded from the calculation of diluted earnings per share: December 31, 2018 2017 2016 Restricted stock awards with performance only targets not yet achieved 1,643,760 1,769,447 1,731,522 Stock options with performance only targets not yet achieved 586,253 586,523 417,086 Anti-dilutive restricted stock awards and restricted stock units 10,296 — 751,410 Anti-dilutive stock options 863,063 621,747 1,381,352

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Options Activity	The following table summarizes the activity of common stock options for the period from the date of the Business Combination of May 4, 2016 through the year ended December 31, 2018 , which includes both the Eco Services Class B Units that were canceled and replaced, as well as the PQ Holdings options that were exchanged as part of the Business Combination: Number of Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Granted/assumed on May 4, 2016 in connection with the Business Combination 1,738,527 $ 7.80 Granted 538,908 $ 8.05 Forfeited (478,997 ) $ 7.49 Outstanding at December 31, 2016 1,798,438 $ 7.96 Granted 1,051,496 $ 13.70 Exercised (32,366 ) $ 8.04 Forfeited (102,398 ) $ 7.98 Outstanding at December 31, 2017 2,715,170 $ 10.18 Granted 241,316 $ 17.50 Exercised (15,332 ) $ 8.51 Outstanding at December 31, 2018 2,941,154 $ 10.79 7.71 $ 14,452 Exercisable at December 31, 2018 1,629,969 $ 10.19 7.71 $ 8,748
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The fair values of PQ Group Holdings common stock options granted during the years ended December 31, 2018 , 2017 and 2016 were determined on the respective grant dates using a Black-Scholes option pricing model with the following weighted-average assumptions: 2018 2017 2016 Expected term (in years) 5.75 5.85 5.00 Expected volatility 26.38 % 34.85 % 45.79 % Risk-free interest rate 2.86 % 2.00 % 1.54 % Expected dividend yield 0.00 % 0.00 % 0.00 % Weighted average grant date fair value of options granted $ 5.47 $ 4.71 $ 3.33
Nonvested Restricted Stock Shares Activity	The following table summarizes the activity of restricted stock awards and restricted stock units for the period from the date of the Business Combination of May 4, 2016 through the year ended December 31, 2018 , which includes the PQ Holdings restricted stock awards that were exchanged as part of the Business Combination: Restricted Stock Awards Restricted Stock Units Number of Weighted Average Grant Date Fair Value (per share) Number of Weighted Average Grant Date Fair Value (per share) Granted/assumed on May 4, 2016 in connection with the Business Combination 2,444,070 $ 9.27 — $ — Granted 266,955 $ 12.32 — $ — Vested (207,915 ) $ 12.32 — $ — Forfeited (20,178 ) $ 10.52 — $ — Nonvested as of December 31, 2016 2,482,932 $ 9.34 — $ — Granted 51,907 $ 16.11 1,654,690 $ 16.97 Vested (187,837 ) $ 12.84 — $ — Forfeited (250,365 ) $ 12.03 — $ — Nonvested as of December 31, 2017 2,096,637 $ 8.87 1,654,690 $ 16.97 Granted 14,498 $ 13.80 161,598 $ 16.12 Vested (223,298 ) $ 12.18 (797,859 ) $ 16.97 Forfeited (117,177 ) $ 8.04 (19,643 ) $ 16.97 Nonvested as of December 31, 2018 1,770,660 $ 8.39 998,786 $ 16.83

Commitments and Contingent Li_2

Commitments and Contingent Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Total rent due under non-cancelable operating lease commitments as of December 31, 2018 is: Year Amount 2019 $ 18,457 2020 14,344 2021 11,432 2022 8,354 2023 6,198 Thereafter 17,477 $ 76,262
Expected Purchases Under Purchase Agreements	The purchase commitments covered by these agreements are with various suppliers and total approximately $56,642 as of December 31, 2018 . Purchases under these agreements are expected to be as follows: Year Amount 2019 $ 28,485 2020 19,820 2021 2,039 2022 1,450 2023 1,305 Thereafter 3,543 $ 56,642

Restructuring and Other Relat_2

Restructuring and Other Related Costs (Tables)	12 Months Ended
	Dec. 31, 2018
Restructuring and Related Activities [Abstract]
Components of Restructuring and Other Related Costs	The following table presents the components of restructuring and other related costs for the years ended December 31, 2018 , 2017 and 2016 included in other operating expense, net, in the accompanying consolidated statements of operations: Years ended 2018 2017 2016 Severance and other employee costs related to Eco Services restructuring plan $ — $ 830 $ 5,093 Severance and other employee costs related to performance materials plant closure 885 4,711 — Other related costs 5,323 2,949 7,537 $ 6,208 $ 8,490 $ 12,630
Rollforward of Restructuring Liabilities	The activity in the accrued liability balance associated with the Company’s restructuring plans, all of which related to severance and other employee costs, was as follows for the years ended December 31, 2018 , 2017 and 2016 : Eco Services Restructuring Plan Performance Materials Plant Closure Total Restructuring Charges Balance at December 31, 2015 $ 1,293 $ — $ 1,293 Restructuring charges 5,093 — 5,093 Cash payments (4,743 ) — (4,743 ) Balance at December 31, 2016 $ 1,643 $ — $ 1,643 Restructuring charges 830 4,711 5,541 Cash payments (2,258 ) (1,588 ) (3,846 ) Balance at December 31, 2017 $ 215 $ 3,123 $ 3,338 Restructuring charges — 581 581 Other adjustments — 304 304 Cash payments (215 ) (2,738 ) (2,953 ) Balance at December 31, 2018 $ — $ 1,270 $ 1,270

Quarterly Financial Summary (_2

Quarterly Financial Summary (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	The following tables summarize the Company’s quarterly financial results during the years ended December 31, 2018 and 2017 : 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Sales $ 366,197 $ 434,713 $ 427,203 $ 380,041 Gross profit 78,121 108,404 107,500 87,609 Operating income 28,189 49,054 48,854 57,459 Net income 556 16,159 14,436 28,470 Net income attributable to PQ Group Holdings Inc. 214 15,782 14,185 28,119 Net income per share: Basic income per share $ 0.00 $ 0.12 $ 0.11 $ 0.21 Diluted income per share $ 0.00 $ 0.12 $ 0.11 $ 0.21 Weighted average shares outstanding: Basic 133,154,144 133,222,463 133,336,352 133,765,294 Diluted 133,884,983 134,209,740 134,576,162 134,987,604 2017 First Quarter Second Quarter Third Quarter Fourth Quarter (1) Sales $ 332,931 $ 389,267 $ 391,829 $ 358,074 Gross profit 82,712 107,414 102,559 84,151 Operating income 37,652 55,080 46,385 26,771 Net income (loss) (2,315 ) (1,670 ) (3,016 ) 65,564 Net income (loss) attributable to PQ Group Holdings Inc. (2,454 ) (1,609 ) (3,345 ) 65,011 Net income (loss) per share: Basic income (loss) per share $ (0.02 ) $ (0.02 ) $ (0.03 ) $ 0.49 Diluted income (loss) per share $ (0.02 ) $ (0.02 ) $ (0.03 ) $ 0.49 Weighted average shares outstanding: Basic 103,947,888 104,015,815 104,096,837 133,138,140 Diluted 103,947,888 104,015,815 104,096,837 133,895,646 (1) Net income includes a provisional net tax benefit of $64,343 as a result of the rate reduction from the TCJA, which was enacted during the quarter ended December 31, 2017 . Refer to Note 19 of these consolidated financial statements for further information.

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	The following table presents supplemental cash flow information for the Company: Years ended December 31, 2018 2017 2016 Cash paid during the year for: Income taxes, net of refunds $ 23,842 $ 29,199 $ 16,981 Interest (1) 105,057 170,131 132,579 Non-cash investing activity: Capital expenditures acquired on account but unpaid as of the year end 23,498 18,762 18,161 Non-cash financing activities: Equity consideration for the Business Combination (Note 7) — — 910,800 Debt assumed in the Business Combination (Note 7) — — 22,911 Debt assumed in the Acquisition (Note 8) — 16,609 — (1) Excludes capitalized interest and the net interest proceeds on swaps designated as net investment hedges, which are included within cash flows from investing activities in the Company’s consolidated statements of cash flows.
Schedule of Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets as of December 31, 2018 , 2017 and 2016 to the total of the same amounts shown in the consolidated statements of cash flows for the years then ended: December 31, 2018 2017 2016 Cash and cash equivalents $ 57,854 $ 66,195 $ 70,742 Restricted cash included in prepaid and other current assets 1,872 1,048 14,335 Total cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows $ 59,726 $ 67,243 $ 85,077
Restrictions on Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets as of December 31, 2018 , 2017 and 2016 to the total of the same amounts shown in the consolidated statements of cash flows for the years then ended: December 31, 2018 2017 2016 Cash and cash equivalents $ 57,854 $ 66,195 $ 70,742 Restricted cash included in prepaid and other current assets 1,872 1,048 14,335 Total cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows $ 59,726 $ 67,243 $ 85,077

Schedule I - Condensed Financ_3

Schedule I - Condensed Financial Information of Parent (Tables)	12 Months Ended
	Dec. 31, 2018
Condensed Financial Information Disclosure [Abstract]
Schedule of Condensed Statements of Operations	Years ended 2018 2017 2016 Stock compensation expense $ 19,464 $ 8,799 $ 7,029 Equity in net (income) loss from subsidiaries (77,764 ) (66,402 ) 72,717 Net income (loss) 58,300 57,603 (79,746 ) Other comprehensive income (loss), net of tax: Pension and postretirement benefits (7,958 ) (101 ) 6,865 Net (loss) gain from hedging activities (330 ) (3,590 ) 4,557 Foreign currency translation (35,127 ) 61,713 (65,781 ) Total other comprehensive income (loss) (43,415 ) 58,022 (54,359 ) Comprehensive income (loss) $ 14,885 $ 115,625 $ (134,105 )
Schedule of Condensed Balance Sheets	December 31, December 31, ASSETS Total current assets $ — $ — Investment in subsidiaries 1,659,560 1,628,000 Total assets $ 1,659,560 $ 1,628,000 LIABILITIES Total current liabilities $ — $ — Total liabilities — — STOCKHOLDERS' EQUITY Common stock ($0.01 par); authorized shares 450,000,000; issued shares 135,758,269 and 135,244,379 on December 31, 2018 and December 31, 2017, respectively; outstanding shares 135,592,045 and 135,244,379 on December 31, 2018 and December 31, 2017, respectively 1,358 1,352 Preferred stock ($0.01 par); authorized shares 50,000,000; no shares issued or outstanding on December 31, 2018 and December 31, 2017 — — Additional paid-in capital 1,674,703 1,655,114 Retained earnings (accumulated deficit) 25,523 (32,777 ) Treasury stock, at cost; shares 166,224 and 0 on December 31, 2018 and 2017, respectively (2,920 ) — Accumulated other comprehensive (loss) income (39,104 ) 4,311 Total PQ Group Holdings Inc. equity 1,659,560 1,628,000 Total liabilities and equity $ 1,659,560 $ 1,628,000
Schedule of Condensed Statements of Cash Flow	CONDENSED STATEMENTS OF CASH FLOWS (in thousands) Years ended 2018 2017 2016 Cash flows from operating activities: Net income (loss) $ 58,300 $ 57,603 $ (79,746 ) Adjustments to reconcile net income (loss) to net cash provided by operating activities: Equity in net (income) loss from subsidiaries (77,764 ) (66,402 ) 72,717 Stock compensation expense 19,464 8,799 7,029 Net cash provided by operating activities — — — Cash flows from investing activities: Investment in subsidiaries — (480,696 ) — Net cash used in investing activities — (480,696 ) — Cash flows from financing activities: IPO proceeds — 507,500 — IPO costs — (26,804 ) — Net cash provided by financing activities — 480,696 — Effect of exchange rate changes on cash, cash equivalents and restricted cash — — — Net change in cash, cash equivalents and restricted cash — — — Cash, cash equivalents and restricted cash at beginning of period — — — Cash, cash equivalents and restricted cash at end of period $ — $ — $ —

Background and Basis of Prese_2

Background and Basis of Presentation (Details) $ / shares in Units, $ in Thousands	Oct. 03, 2017USD ($)$ / sharesshares	Sep. 28, 2017	Dec. 31, 2018segment	Sep. 29, 2017$ / shares
Subsidiary or Equity Method Investee
Reportable segments | segment			2
Stock split, conversion ratio		8.8275
Unreturned paid-in capital per share (usd per share)				$ 113.74
IPO
Subsidiary or Equity Method Investee
Price of shares issued (usd per share)	$ 17.50
Shares issued (shares) | shares	29,000,000
Consideration received | $	$ 480,696

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narratives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of Significant Accounting Policies Table
Foreign currency exchange loss (gain)	$ 13,810	$ 25,786	$ (3,558)
Restricted cash included in prepaid and other current assets	1,872	1,048	14,335
Interest costs capitalized	3,542	5,806	5,687
Research and development cost	$ 15,565	$ 13,859	$ 7,266
Building and building improvements | Minimum
Summary of Significant Accounting Policies Table
Fixed asset useful life	15 years
Building and building improvements | Maximum
Summary of Significant Accounting Policies Table
Fixed asset useful life	33 years
Machinery and equipment | Minimum
Summary of Significant Accounting Policies Table
Fixed asset useful life	3 years
Machinery and equipment | Maximum
Summary of Significant Accounting Policies Table
Fixed asset useful life	10 years

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Asset Retirement Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Asset Retirement Obligation
Beginning balance	$ 4,094	$ 3,700
Accretion expense	287	232
Foreign exchange impact	(157)	162
Ending balance	$ 4,224	$ 4,094

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Cash Flow Hedge Impact on AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Cost of goods sold	$ (1,226,520)	$ (1,095,265)	$ (810,085)
Interest (expense) income	$ (113,723)	$ (179,044)	$ (140,315)

New Accounting Standards (Detai

New Accounting Standards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle
Pension benefit included in other expense (income), net	$ 3,625	$ 1,616	$ 2,651
Restricted cash included in prepaid and other current assets	$ 1,872	$ 1,048	$ 14,335

New Accounting Standards - Adju

New Accounting Standards - Adjustment Disclosure (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle
Net cash provided by (used in) operating activities	$ 248,644	$ 165,173	$ 122,708
Net cash provided by (used in) investing activities(2)	(119,290)	(195,982)	(1,915,763)
Net cash provided by (used in) financing activities(1)	(137,225)	19,833	1,858,445
Effect of exchange rate changes on cash, cash equivalents and restricted cash	354	(6,858)	(5,886)
Net change in cash, cash equivalents and restricted cash	(7,517)	(17,834)	59,504
Cash, cash equivalents and restricted cash at beginning of period	67,243	85,077	25,573
Cash, cash equivalents and restricted cash at end of period	59,726	67,243	85,077
Debt prepayment penalties	0	47,875	0
Payments of debt issuance costs	6,395	4,666	23,786
Accounting Standards Update 2016-15 and 2016-18 | Previously Reported
New Accounting Pronouncements or Change in Accounting Principle
Net cash provided by (used in) operating activities		116,062	119,720
Net cash provided by (used in) investing activities(2)		(182,695)	(1,929,680)
Net cash provided by (used in) financing activities(1)		68,944	1,861,433
Effect of exchange rate changes on cash, cash equivalents and restricted cash		(6,858)	(5,886)
Net change in cash, cash equivalents and restricted cash		(4,547)	45,587
Cash, cash equivalents and restricted cash at beginning of period	66,195	70,742	25,155
Cash, cash equivalents and restricted cash at end of period		66,195	70,742
Accounting Standards Update 2016-15 and 2016-18 | Adjustments
New Accounting Pronouncements or Change in Accounting Principle
Net cash provided by (used in) operating activities		49,111	2,988
Net cash provided by (used in) investing activities(2)		(13,287)	13,917
Net cash provided by (used in) financing activities(1)		(49,111)	(2,988)
Effect of exchange rate changes on cash, cash equivalents and restricted cash		0	0
Net change in cash, cash equivalents and restricted cash		(13,287)	13,917
Cash, cash equivalents and restricted cash at beginning of period	$ 1,048	14,335	418
Cash, cash equivalents and restricted cash at end of period		1,048	14,335
Debt prepayment penalties		47,875
Payments of debt issuance costs		$ (1,236)	$ (2,988)

Revenue from Contracts with C_3

Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Sales	$ 380,041	$ 427,203	$ 434,713	$ 366,197	$ 358,074	$ 391,829	$ 389,267	$ 332,931	$ 1,608,154	$ 1,472,101	$ 1,064,177
Operating segments
Disaggregation of Revenue [Line Items]
Sales									1,611,477
Operating segments | Industrial & chemical process
Disaggregation of Revenue [Line Items]
Sales									357,630
Operating segments | Fuels & emission control
Disaggregation of Revenue [Line Items]
Sales									246,452
Operating segments | Packaging & engineered plastics
Disaggregation of Revenue [Line Items]
Sales									262,177
Operating segments | Highway safety & construction
Disaggregation of Revenue [Line Items]
Sales									320,134
Operating segments | Consumer products
Disaggregation of Revenue [Line Items]
Sales									272,576
Operating segments | Natural resources
Disaggregation of Revenue [Line Items]
Sales									152,508
Inter-segment sales eliminations
Disaggregation of Revenue [Line Items]
Sales									(3,323)	(3,423)	(1,521)
Environmental Catalysts & Services
Disaggregation of Revenue [Line Items]
Sales									524,338
Environmental Catalysts & Services | Operating segments
Disaggregation of Revenue [Line Items]
Sales									527,661	473,675	426,747
Environmental Catalysts & Services | Operating segments | Industrial & chemical process
Disaggregation of Revenue [Line Items]
Sales									77,952
Environmental Catalysts & Services | Operating segments | Fuels & emission control
Disaggregation of Revenue [Line Items]
Sales									246,452
Environmental Catalysts & Services | Operating segments | Packaging & engineered plastics
Disaggregation of Revenue [Line Items]
Sales									131,181
Environmental Catalysts & Services | Operating segments | Highway safety & construction
Disaggregation of Revenue [Line Items]
Sales									0
Environmental Catalysts & Services | Operating segments | Consumer products
Disaggregation of Revenue [Line Items]
Sales									0
Environmental Catalysts & Services | Operating segments | Natural resources
Disaggregation of Revenue [Line Items]
Sales									72,076
Environmental Catalysts & Services | Inter-segment sales eliminations
Disaggregation of Revenue [Line Items]
Sales									(3,323)
Performance Materials & Chemicals
Disaggregation of Revenue [Line Items]
Sales									1,083,816
Performance Materials & Chemicals | Operating segments
Disaggregation of Revenue [Line Items]
Sales									1,083,816	$ 1,001,849	$ 638,951
Performance Materials & Chemicals | Operating segments | Industrial & chemical process
Disaggregation of Revenue [Line Items]
Sales									279,678
Performance Materials & Chemicals | Operating segments | Fuels & emission control
Disaggregation of Revenue [Line Items]
Sales									0
Performance Materials & Chemicals | Operating segments | Packaging & engineered plastics
Disaggregation of Revenue [Line Items]
Sales									130,996
Performance Materials & Chemicals | Operating segments | Highway safety & construction
Disaggregation of Revenue [Line Items]
Sales									320,134
Performance Materials & Chemicals | Operating segments | Consumer products
Disaggregation of Revenue [Line Items]
Sales									272,576
Performance Materials & Chemicals | Operating segments | Natural resources
Disaggregation of Revenue [Line Items]
Sales									80,432
Performance Materials & Chemicals | Inter-segment sales eliminations
Disaggregation of Revenue [Line Items]
Sales									$ 0

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets:
Derivative contracts	$ 20,768	$ 1,043
Restoration plan assets	4,244	5,576
Total	25,012	6,619
Liabilities:
Derivative contracts	2,026	448
Recurring | Quoted Prices in Active Markets (Level 1)
Assets:
Derivative contracts	0	0
Restoration plan assets	4,244	5,576
Total	4,244	5,576
Liabilities:
Derivative contracts	0	0
Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Derivative contracts	20,768	1,043
Restoration plan assets	0	0
Total	20,768	1,043
Liabilities:
Derivative contracts	2,026	448
Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Derivative contracts	0	0
Restoration plan assets	0	0
Total	0	0
Liabilities:
Derivative contracts	$ 0	$ 0

Fair Value Measurements - Ass_2

Fair Value Measurements - Assets Measured at Fair Value on a Non-recurring Basis (Details) - USD ($) $ in Thousands	Oct. 01, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Intangible asset impairment charge		$ 0	$ 0	$ 6,873
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Indefinite-lived trade names	$ 153,922
Indefinite-lived intangible assets, gross	160,795
Intangible asset impairment charge	$ 6,873
Estimate of Fair Value Measurement | Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Indefinite-lived trade names				153,922
Estimate of Fair Value Measurement | Nonrecurring | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Indefinite-lived trade names				0
Estimate of Fair Value Measurement | Nonrecurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Indefinite-lived trade names				0
Estimate of Fair Value Measurement | Nonrecurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Indefinite-lived trade names				153,922
Change Measurement During Period | Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Indefinite-lived trade names				$ (6,873)

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Components, Net of Tax (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss), Net of Tax
Stockholders equity	$ 1,664,145	$ 1,631,919	$ 1,027,944	$ 235,293
Accumulated other comprehensive income (loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax
Stockholders equity	(39,104)	4,311	(53,711)	$ 648
Defined benefit and other postretirement plans
Accumulated Other Comprehensive Income (Loss), Net of Tax
Stockholders equity	(546)	7,412	7,513
Tax
Tax related to AOCI	(2,362)	(4,761)
Net gain (loss) from hedging activities
Accumulated Other Comprehensive Income (Loss), Net of Tax
Stockholders equity	637	967	4,557
Tax
Tax related to AOCI	(474)	(584)
Foreign currency translation
Accumulated Other Comprehensive Income (Loss), Net of Tax
Stockholders equity	(39,195)	(4,068)	$ (65,781)
Tax
Tax related to AOCI	$ 5,154	$ 790

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Pre-tax and After-tax Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
After-tax amount
Pre-tax amount	$ (50,217)	$ 60,500	$ (54,447)
Tax benefit / (expense)	6,873	(3,590)	(965)
Total other comprehensive income (loss)	(43,344)	56,910	(55,412)
Defined benefit and other postretirement plans
After-tax amount
Pre-tax amount	(10,357)	(139)	11,664
Tax benefit / (expense)	2,399	38	(4,799)
Total other comprehensive income (loss)	(7,958)	(101)	6,865
Net loss (gain) from hedging activities
After-tax amount
Pre-tax amount	(441)	(5,799)	7,350
Tax benefit / (expense)	110	2,209	(2,793)
Total other comprehensive income (loss)	(331)	(3,590)	4,557
Foreign currency translation
After-tax amount
Pre-tax amount	(39,419)	66,438	(73,461)
Tax benefit / (expense)	4,364	(5,837)	6,627
Total other comprehensive income (loss)	$ (35,055)	$ 60,601	$ (66,834)

Accumulated Other Comprehensi_5

Accumulated Other Comprehensive Income (Loss) - Change by Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance, value	$ 1,631,919	$ 1,027,944	$ 235,293
Amounts reclassified from accumulated other comprehensive income	(157)	100
Total other comprehensive income (loss)	(43,344)	56,910	(55,412)
Ending balance, value	1,664,145	1,631,919	1,027,944
Total
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance, value	4,311	(53,711)	648
Other comprehensive income (loss) before reclassifications	(43,258)	57,922
Amounts reclassified from accumulated other comprehensive income	(157)	100
Total other comprehensive income (loss)	(43,415)	58,022	(54,359)
Ending balance, value	(39,104)	4,311	(53,711)
Defined benefit and other postretirement plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance, value	7,412	7,513
Other comprehensive income (loss) before reclassifications	(7,874)	6
Amounts reclassified from accumulated other comprehensive income	(84)	(107)
Total other comprehensive income (loss)	(7,958)	(101)
Ending balance, value	(546)	7,412	7,513
Net gain (loss) from hedging activities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance, value	967	4,557
Other comprehensive income (loss) before reclassifications	(257)	(3,797)
Amounts reclassified from accumulated other comprehensive income	(73)	207
Total other comprehensive income (loss)	(330)	(3,590)
Ending balance, value	637	967	4,557
Foreign currency translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax
Beginning balance, value	(4,068)	(65,781)
Other comprehensive income (loss) before reclassifications	(35,127)	61,713
Amounts reclassified from accumulated other comprehensive income	0	0
Total other comprehensive income (loss)	(35,127)	61,713
Ending balance, value	$ (39,195)	$ (4,068)	$ (65,781)

Accumulated Other Comprehensi_6

Accumulated Other Comprehensive Income (Loss) - Reclassifications out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification, net									$ (157)	$ 100
Interest expense, net									113,723	179,044	$ 140,315
Cost of goods sold									1,226,520	1,095,265	810,085
Income (loss) before income taxes and noncontrolling interest									(88,616)	60,634	69,117
Tax (expense) benefit									28,995	(119,197)	10,041
Net (income) loss	$ (28,470)	$ (14,436)	$ (16,159)	$ (556)	$ (65,564)	$ 3,016	$ 1,670	$ 2,315	(59,621)	(58,563)	$ 79,158
Defined benefit and other postretirement plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification, before tax									(100)	(132)
Reclassification, tax									16	25
Reclassification, net									(84)	(107)
Amortization of prior service cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification, before tax									(112)	(78)
Amortization of net gain (loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification, before tax									12	(54)
Net gain (loss) from hedging activities | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes and noncontrolling interest									(97)	262
Tax (expense) benefit									24	(55)
Net (income) loss									(73)	207
Net gain (loss) from hedging activities | Reclassification out of Accumulated Other Comprehensive Income | Interest rate caps
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense, net									256	40
Net gain (loss) from hedging activities | Reclassification out of Accumulated Other Comprehensive Income | Natural gas swaps
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Cost of goods sold									$ (353)	$ 222

Business Combination - Narrativ

Business Combination - Narratives (Details) - USD ($) $ in Thousands	May 04, 2016	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition
Net income (loss)		$ 28,470	$ 14,436	$ 16,159	$ 556	$ 65,564	$ (3,016)	$ (1,670)	$ (2,315)		$ 59,621	$ 58,563	$ (79,158)
Debt Repayment Penalty
Business Acquisition
Net income (loss)													(26,250)
Refinancing Charges
Business Acquisition
Net income (loss)													(4,747)
Transaction Fees
Business Acquisition
Net income (loss)													(1,795)
PQ Holdings, Eco Services
Business Acquisition
Payments to acquire business	$ 1,777,740
Equity consideration for the business combination	910,800										$ 0	0	910,800
Stock awards transferred as consideration	1,400
Acquisition costs													1,583
Increase to inventory at acquisition	$ 58,683
Cost of goods sold, additional portion related to step-up inventory price												$ 871	$ 29,086
Sales attributable to acquiree										$ 690,459
Net income (loss) from acquiree										$ 17,991

Business Combination - Business

Business Combination - Business Acquired (Details) - USD ($) $ in Thousands	May 04, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition
Total consideration, net of cash acquired		$ 1,006	$ 41,572	$ 1,777,740
Recognized amounts of identifiable assets acquired and liabilities assumed:
Goodwill		$ 1,254,929	$ 1,305,956	$ 1,241,429
PQ Holdings, Eco Services
Business Acquisition
Total consideration, net of cash acquired	$ 2,689,941
Recognized amounts of identifiable assets acquired and liabilities assumed:
Receivables	161,110
Inventories	254,770
Prepaid and other current assets	19,295
Investments in affiliated companies	472,994
Property, plant and equipment	683,673
Other intangible assets	754,000
Other long-term assets	48,127
Fair value of assets acquired	2,393,969
Revolver, notes payable & current debt	(2,441)
Accounts payable	(93,222)
Accrued liabilities	(98,621)
Long-term debt	(20,470)
Deferred income taxes	(327,296)
Other long-term liabilities	(113,936)
Noncontrolling interest	(6,569)
Fair value of net assets acquired	1,731,414
Goodwill	958,527
Net assets including goodwill acquired	$ 2,689,941

Business Combination - Intangib

Business Combination - Intangible Assets Acquired (Details) - PQ Holdings, Eco Services $ in Thousands	May 04, 2016USD ($)
Business Acquisition
Intangible assets subject to amortization:	$ 520,000
Total	754,000
Trade names
Business Acquisition
Intangible assets not subject to amortization	151,100
Trademarks
Business Acquisition
Intangible assets not subject to amortization	82,900
Trademarks
Business Acquisition
Intangible assets subject to amortization:	$ 35,400
Finite lived intangible assets useful life	15 years
Technical know-how
Business Acquisition
Intangible assets subject to amortization:	$ 189,300
Finite lived intangible assets useful life	20 years
Contracts
Business Acquisition
Intangible assets subject to amortization:	$ 19,800
Finite lived intangible assets useful life	5 years 3 months 18 days
Customer relationships
Business Acquisition
Intangible assets subject to amortization:	$ 268,700
Finite lived intangible assets useful life	10 years 7 months 6 days
In-process research and development
Business Acquisition
Intangible assets subject to amortization:	$ 6,800

Business Combination - Proforma

Business Combination - Proforma Disclosure (Details) - PQ Holdings, Eco Services $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)
Business Acquisition
Pro forma sales	$ 1,403,041
Pro forma net loss	$ (76,994)

Acquisition - Allocation of Pur

Acquisition - Allocation of Purchase Price (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 12, 2017	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition
Total consideration, net of cash acquired				$ 1,006	$ 41,572	$ 1,777,740
Recognized amounts of identifiable assets acquired and liabilities assumed:
Goodwill				1,254,929	$ 1,305,956	$ 1,241,429
Sovitec Mondial S.A.
Business Acquisition
Total consideration, net of cash acquired	$ 41,572	$ 41,572
Measurement period adjustments, total consideration, net of cash acquired			$ 0
Recognized amounts of identifiable assets acquired and liabilities assumed:
Receivables	14,305	14,305	14,305
Measurement period adjustments, receivables			0
Inventories	9,248	7,645	9,248
Measurement period adjustments, inventories			1,603	$ 1,603
Prepaid and other current assets	400	400	400
Measurement period adjustments, prepaid and other current assets			0
Property, plant and equipment	24,980	9,020	24,980
Measurement period adjustments, property, plant and equipment			15,960
Other intangible assets	5,753	0	5,753
Measurement period adjustments, other intangible assets			5,753
Other long-term assets	16,050	129	16,050
Measurement period adjustments, other long-term assets			15,921
Fair value of assets acquired	70,736	31,499	70,736
Measurement period adjustments, fair value of assets acquired			39,237
Current debt	(6,420)	(6,420)	(6,420)
Measurement period adjustments, current debt			0
Accounts payable	(10,748)	(10,748)	(10,748)
Measurement period adjustments, accounts payable			0
Long-term debt	(10,189)	(10,189)	(10,189)
Measurement period adjustments, long-term debt			0
Deferred income taxes	(4,426)	0	(4,426)
Measurement period adjustments, deferred income taxes			(4,426)
Other long-term liabilities	(154)	(154)	(154)
Measurement period adjustments, other long-term liabilities			0
Fair value of net assets acquired	38,799	3,988	38,799
Measurement period adjustments, fair value of net assets acquired			34,811
Goodwill	2,773	37,584	2,773
Measurement period adjustments, goodwill			(34,811)
Net assets including goodwill acquired	$ 41,572	$ 41,572	41,572
Measurement period adjustments, net assets including goodwill acquired			$ 0

Acquisition - Narratives (Detai

Acquisition - Narratives (Details) - USD ($) $ in Thousands	3 Months Ended	10 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 12, 2017
Intangible asset amortization
Business Acquisition
Net income (loss)				$ 367	$ 364
Property, plant, and equipment depreciation
Business Acquisition
Net income (loss)				760	467
Sovitec Mondial S.A.
Business Acquisition
Gross contractual amount of accounts receivable acquired						$ 14,607
Uncollectable accounts receivable acquired						$ 302
Measurement period adjustments, inventories		$ 1,603	$ 1,603
Measurement period adjustments, depreciation			421
Measurement period adjustments, income tax benefit			(990)
Net income (loss)				58,774	$ (78,234)
Acquisition costs				$ 2,515
Sovitec Mondial S.A. | Acquisition-related costs
Business Acquisition
Net income (loss)	$ 2,515
Cost of goods sold | Sovitec Mondial S.A.
Business Acquisition
Measurement period adjustments, amortization			108
Other expense, net | Sovitec Mondial S.A.
Business Acquisition
Measurement period adjustments, amortization			$ 101

Acquisition - Intangible Assets

Acquisition - Intangible Assets Acquired (Details) - Sovitec Mondial S.A. - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Jun. 12, 2017
Business Acquisition [Line Items]
Intangible assets subject to amortization	$ 3,659
Total	5,753	$ 0
Trademarks
Business Acquisition [Line Items]
Intangible assets subject to amortization	$ 1,767
Weighted average expected useful life (in years)	11 years
Technical know-how
Business Acquisition [Line Items]
Intangible assets subject to amortization	$ 1,892
Weighted average expected useful life (in years)	11 years
Trade names
Business Acquisition [Line Items]
Trade names, not subject to amortization	$ 2,094

Acquisition - Pro Forma Disclos

Acquisition - Pro Forma Disclosure (Details) - Sovitec Mondial S.A. - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition
Pro forma sales	$ 1,488,528	$ 1,105,479
Pro forma net income (loss)	58,774	(78,234)
Pro forma net income (loss) attributable to PQ Group Holdings Inc.	$ 57,814	$ (78,822)
Pro forma basic income (loss) per share	$ 0.52	$ (1.01)
Pro forma diluted income (loss) per share	$ 0.52	$ (1.01)

Other Operating Expense, Net (D

Other Operating Expense, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Income and Expenses [Abstract]
Amortization expense	$ 35,025	$ 32,010	$ 25,263
Transaction and other related costs	776	7,415	4,952
Restructuring and other related costs	6,208	8,490	12,630
Net loss on asset disposals	6,574	5,793	4,216
Intangible asset impairment charge	0	0	6,873
Management advisory fees	0	3,777	3,584
Insurance recoveries	(5,480)	0	0
Write-off of long-term supply contract obligation	(20,612)	0	0
Other, net	6,959	6,740	4,783
Other operating expense, net	29,450	$ 64,225	$ 62,301
Total gain related to insurance recoveries	(6,450)
Insurance recoveries recorded as gain on asset disposals	207
Insurance recoveries recorded as non-operating income	$ 813

Inventories (Details)

Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventory, Net
Finished products and work in process	$ 206,188	$ 199,919
Raw materials	58,560	62,469
Inventory, Net	264,748	262,388
Valued at lower of cost or market:
LIFO basis	160,863	162,315
Valued at Lower of Cost and Net Realizable Value [Abstract]
FIFO or average cost basis	103,885	100,073
Inventory, Net	$ 264,748	$ 262,388

Inventories - Narratives (Detai

Inventories - Narratives (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Business Combinations
Inventory
Difference in LIFO and FIFO inventory valuation	$ 18,263	$ 26,630

Investments in Affiliated Com_3

Investments in Affiliated Companies - Ownership Percentage (Details)	Dec. 31, 2018
PQ Silicates Ltd.
Schedule of Equity Method Investments [Line Items]
Ownership percentage	50.00%
Zeolyst International
Schedule of Equity Method Investments [Line Items]
Ownership percentage	50.00%
Zeolyst C.V.
Schedule of Equity Method Investments [Line Items]
Ownership percentage	50.00%
Quaker Holdings
Schedule of Equity Method Investments [Line Items]
Ownership percentage	49.00%
Aetec
Schedule of Equity Method Investments [Line Items]
Ownership percentage	20.00%

Investments in Affiliated Com_4

Investments in Affiliated Companies - Summarized Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Current assets	$ 215,416	$ 213,815
Noncurrent assets	248,288	235,440
Current liabilities	40,536	37,018
Noncurrent liabilities	$ 56	$ 1,417

Investments in Affiliated Com_5

Investments in Affiliated Companies - Summarized Income Statement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Method Investment, Summarized Financial Information
Net sales	$ 352,599	$ 317,197	$ 206,072
Gross profit	126,945	132,812	91,761
Operating income	88,508	91,224	67,098
Net income	$ 88,622	$ 94,740	$ 67,332

Investments in Affiliated Com_6

Investments in Affiliated Companies - Narratives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition
Charges related to purchase accounting fair value adjustments	$ 6,634	$ 8,599	$ 36,296
Equity Method Investee
Business Acquisition
Due from related parties	4,775	4,910
Related party sales	2,823	2,853	1,587
Purchases from related party	645	2,475	$ 1,147
Business Combination
Business Acquisition
Purchase accounting fair value adjustments	$ 258,066	$ 264,700

Investments in Affiliated Com_7

Investments in Affiliated Companies - Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity Method Investments
Balance at beginning of period	$ 469,276	$ 459,406
Investments in affiliated companies	5,000	9,000	$ 0
Equity in net income of affiliated companies	44,245	47,371
Charges related to purchase accounting fair value adjustments	(6,634)	(8,599)	(36,296)
Dividends received	(40,890)	(44,071)
Foreign currency translation adjustments	(2,786)	6,050
Balance at end of period	468,211	469,276	$ 459,406
Sovitec Mondial S.A.
Equity Method Investments
Equity method investments assumed in business combination	$ 0	$ 119

Property, Plant and Equipment_2

Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,630,358	$ 1,541,499
Less: accumulated depreciation	(421,379)	(311,115)
Property, plant and equipment, net	1,208,979	1,230,384
Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	190,772	191,006
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	212,284	200,054
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,125,117	1,005,025
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 102,185	$ 145,414

Property, Plant and Equipment -

Property, Plant and Equipment - Narratives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Depreciation	$ 132,640	$ 124,551	$ 89,453

Reportable Segments - Narrative

Reportable Segments - Narratives (Details)	12 Months Ended
	Dec. 31, 2018segmentproduct_group	Dec. 31, 2017segment
Segment Reporting Information
Number of operating segments	2	2,000
Reportable segments	2
Environmental Catalysts & Services
Segment Reporting Information
Number of product groups | product_group	3

Reportable Segments - Summary F

Reportable Segments - Summary Financial Information by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales	$ 380,041	$ 427,203	$ 434,713	$ 366,197	$ 358,074	$ 391,829	$ 389,267	$ 332,931	$ 1,608,154	$ 1,472,101	$ 1,064,177
Segment Adjustment EBITDA									386,252	294,590	198,898
Equity in net income (loss) from affiliated companies									37,611	38,772	(2,612)
Performance Materials & Chemicals
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									1,083,816
Environmental Catalysts & Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									524,338
Environmental Catalysts & Services | Zeolyst Joint Venture
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment Adjustment EBITDA									56,663	58,156	39,903
Equity in net income (loss) from affiliated companies									42,854	46,252	(3,313)
Investment in affiliate and inventory step-up amortization									6,634	8,600	36,296
Joint venture depreciation, amortization, and interest									12,592	11,070	6,920
Operating segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									1,611,477
Segment Adjustment EBITDA									500,923	483,715	355,504
Operating segments | Performance Materials & Chemicals
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									1,083,816	1,001,849	638,951
Segment Adjustment EBITDA									243,357	240,128	158,679
Operating segments | Environmental Catalysts & Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									527,661	473,675	426,747
Segment Adjustment EBITDA									257,566	243,587	196,825
Operating segments | Environmental Catalysts & Services | Zeolyst Joint Venture
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									156,687	143,774	94,516
Operating segments | Reportable Subsegment | Performance Materials & Chemicals | Performance Chemicals
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									717,335	687,645	437,523
Operating segments | Reportable Subsegment | Performance Materials & Chemicals | Performance Materials
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									378,279	324,225	206,522
Operating segments | Reportable Subsegment | Environmental Catalysts & Services | Silica Catalysts
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									72,099	75,333	53,029
Operating segments | Reportable Subsegment | Environmental Catalysts & Services | Refining Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									455,562	398,342	373,718
Operating segments | Eliminations | Performance Materials & Chemicals
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									(11,798)	(10,021)	(5,094)
Inter-segment sales eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									(3,323)	$ (3,423)	$ (1,521)
Inter-segment sales eliminations | Performance Materials & Chemicals
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									0
Inter-segment sales eliminations | Environmental Catalysts & Services
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales									$ (3,323)

Reportable Segments - Reconcili

Reportable Segments - Reconciliation of Net Income (Loss) to Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information
Net income (loss) attributable to PQ Group Holdings Inc.	$ 28,119	$ 14,185	$ 15,782	$ 214	$ 65,011	$ (3,345)	$ (1,609)	$ (2,454)	$ 58,300	$ 57,603	$ (79,746)
Provision (benefit) for income taxes									28,995	(119,197)	10,041
Interest expense, net									113,723	179,044	140,315
Depreciation and amortization									185,234	177,140	128,288
Segment EBITDA									386,252	294,590	198,898
Debt extinguishment costs (Note 16)									7,751	61,886	13,782
Losses on disposal of fixed assets									6,574	5,793	4,216
Foreign currency exchange loss (gain)									13,810	25,786	(3,558)
Management advisory fees									0	3,777	3,584
Equity-based and other non-cash compensation									19,464	8,799	7,029
Restructuring, integration and business optimization expenses									581	5,541	5,093
Gain on contract termination									(20,612)	0	0
Corporate, non-segment
Segment Reporting Information
Unallocated corporate expenses									36,970	30,422	23,971
Segment reconciling items
Segment Reporting Information
Joint venture depreciation, amortization, and interest									12,592	11,070	6,920
Investment in affiliate and inventory step-up amortization									6,634	8,600	36,296
Amortization of inventory step-up									1,603	871	29,086
Impairment of fixed assets, intangibles and goodwill									0	0	6,873
Debt extinguishment costs (Note 16)									7,751	61,886	13,782
Losses on disposal of fixed assets									6,574	5,793	4,216
Foreign currency exchange loss (gain)									13,810	25,786	(3,558)
Non-cash revaluation of inventory, including LIFO									8,366	3,708	1,310
Management advisory fees									0	3,777	3,583
Transaction and other related costs									893	7,425	4,664
Equity-based and other non-cash compensation									19,464	8,799	7,042
Restructuring, integration and business optimization expenses									14,019	13,174	16,258
Defined benefit pension plan cost									(796)	2,940	1,375
Gain on contract termination									(20,612)	0	0
Other									7,403	4,874	4,788
Operating segments
Segment Reporting Information
Segment EBITDA									$ 500,923	$ 483,715	$ 355,504

Reportable Segments - Capital E

Reportable Segments - Capital Expenditures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets
Capital expenditure	$ 131,688	$ 140,482	$ 121,421
Operating segments | Performance Materials & Chemicals
Revenues from External Customers and Long-Lived Assets
Capital expenditures gross	75,476	84,783	71,293
Operating segments | Environmental Catalysts & Services
Revenues from External Customers and Long-Lived Assets
Capital expenditures gross	55,007	53,145	57,803
Eliminations
Revenues from External Customers and Long-Lived Assets
Capital expenditures gross	$ 1,205	$ 2,554	$ (7,675)

Reportable Segments - Sales by

Reportable Segments - Sales by Geography (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets
Sales	$ 380,041	$ 427,203	$ 434,713	$ 366,197	$ 358,074	$ 391,829	$ 389,267	$ 332,931	$ 1,608,154	$ 1,472,101	$ 1,064,177
United States
Revenues from External Customers and Long-Lived Assets
Sales									963,722	874,764	705,348
Netherlands
Revenues from External Customers and Long-Lived Assets
Sales									127,803	118,567	79,821
United Kingdom
Revenues from External Customers and Long-Lived Assets
Sales									119,586	116,410	67,494
Other foreign countries
Revenues from External Customers and Long-Lived Assets
Sales									$ 397,043	$ 362,360	$ 211,514

Reportable Segments - Assets by

Reportable Segments - Assets by Geography (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets
Long-lived assets	$ 1,208,979	$ 1,230,384
United States
Revenues from External Customers and Long-Lived Assets
Long-lived assets	865,799	891,861
Netherlands
Revenues from External Customers and Long-Lived Assets
Long-lived assets	52,461	52,882
United Kingdom
Revenues from External Customers and Long-Lived Assets
Long-lived assets	90,095	90,536
Other foreign countries
Revenues from External Customers and Long-Lived Assets
Long-lived assets	$ 200,624	$ 195,105

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Goodwill Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill
Beginning balance	$ 1,305,956	$ 1,241,429
Goodwill recognized	649	37,584
Goodwill adjustments	(34,811)
Foreign exchange impact	(16,865)	26,943
Ending balance	1,254,929	1,305,956
Environmental Catalysts & Services
Goodwill
Beginning balance	391,333	388,923
Goodwill recognized	0	0
Goodwill adjustments	0
Foreign exchange impact	(1,682)	2,410
Ending balance	389,651	391,333
Performance Materials & Chemicals
Goodwill
Beginning balance	914,623	852,506
Goodwill recognized	649	37,584
Goodwill adjustments	(34,811)
Foreign exchange impact	(15,183)	24,533
Ending balance	$ 865,278	$ 914,623

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Narratives (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)segmentreporting_unit	Dec. 31, 2017USD ($)segmentreporting_unit	Dec. 31, 2016USD ($)
Goodwill
Number of reporting units | reporting_unit	4	4,000
Number of operating segments | segment	2	2,000
Goodwill	$ 1,254,929	$ 1,305,956	$ 1,241,429
Intangible asset impairment charge	0	0	6,873
Amortization of intangible assets included in other operating expense, net	35,025	32,010	25,263
Cost of goods sold
Goodwill
Amortization of intangible assets included in cost of goods sold	17,569	20,579	13,573
Other operating expenses
Goodwill
Amortization of intangible assets included in other operating expense, net	35,025	32,010	25,263
Performance Chemicals | Trade names
Goodwill
Intangible asset impairment charge			5,350
Silica Catalysts | Trade names
Goodwill
Intangible asset impairment charge			1,523
Performance Materials & Chemicals
Goodwill
Goodwill	$ 865,278	$ 914,623	$ 852,506

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Definite-lived Intangible assets, net
Accumulated Amortization	$ (154,533)	$ (103,726)
Net Balance	483,241
Indefinite-lived intangible assets
Gross Carrying Amount	882,969	889,870
Net Balance	728,436	786,144
Indefinite-lived trade names
Indefinite-lived intangible assets
Gross Carrying Amount	157,813	158,059
Net Balance	157,813	158,059
Trademarks
Indefinite-lived intangible assets
Gross Carrying Amount	80,582	82,289
Net Balance	80,582	82,289
In-process research and development
Indefinite-lived intangible assets
Gross Carrying Amount	6,800	6,800
Net Balance	6,800	6,800
Finite-Lived Intangible Assets
Definite-lived Intangible assets, net
Gross Carrying Amount	637,774	642,722
Accumulated Amortization	(154,533)	(103,726)
Net Balance	483,241	538,996
Technical know-how
Definite-lived Intangible assets, net
Gross Carrying Amount	211,067	212,599
Accumulated Amortization	(32,112)	(21,138)
Net Balance	$ 178,955	191,461
Technical know-how | Minimum
Indefinite-lived intangible assets
Finite lived intangible assets useful life	11 years
Technical know-how | Maximum
Indefinite-lived intangible assets
Finite lived intangible assets useful life	20 years
Customer relationships
Definite-lived Intangible assets, net
Gross Carrying Amount	$ 361,150	366,021
Accumulated Amortization	(95,399)	(63,860)
Net Balance	$ 265,751	302,161
Customer relationships | Minimum
Indefinite-lived intangible assets
Finite lived intangible assets useful life	7 years
Customer relationships | Maximum
Indefinite-lived intangible assets
Finite lived intangible assets useful life	15 years
Contracts
Definite-lived Intangible assets, net
Gross Carrying Amount	$ 19,800	19,800
Accumulated Amortization	(13,139)	(9,205)
Net Balance	$ 6,661	10,595
Contracts | Minimum
Indefinite-lived intangible assets
Finite lived intangible assets useful life	2 years
Contracts | Maximum
Indefinite-lived intangible assets
Finite lived intangible assets useful life	16 years
Trademarks
Definite-lived Intangible assets, net
Gross Carrying Amount	$ 36,657	35,202
Accumulated Amortization	(6,451)	(3,911)
Net Balance	$ 30,206	31,291
Trademarks | Maximum
Indefinite-lived intangible assets
Finite lived intangible assets useful life	15 years
Permits
Definite-lived Intangible assets, net
Gross Carrying Amount	$ 9,100	9,100
Accumulated Amortization	(7,432)	(5,612)
Net Balance	$ 1,668	$ 3,488
Indefinite-lived intangible assets
Finite lived intangible assets useful life	5 years

Goodwill and Other Intangible_6

Goodwill and Other Intangible Assets - Future Amortization (Details) $ in Thousands	Dec. 31, 2018USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity
2,019	$ 50,652
2,020	47,101
2,021	46,159
2,022	46,092
2,023	42,175
Thereafter	251,062
Total estimated future aggregate amortization expense	$ 483,241

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Compensation and bonus	$ 52,296	$ 49,988
Interest	21,933	15,936
Property tax	3,018	1,622
Environmental reserves (see Note 23)	4,693	5,790
Supply contract obligation (see Note 25)	0	1,638
Income taxes	2,123	1,166
Commissions and rebates	1,798	1,820
Pension, postretirement and supplemental retirement plans (see Note 20)	2,439	2,192
Other	11,709	13,765
Total	$ 100,009	$ 93,917

Long-term Debt (Details)

Long-term Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 11, 2017	Nov. 14, 2016	May 04, 2016
Debt Instrument [Line Items]
Document Period End Date	Dec. 31, 2018
Total debt	$ 2,148,423	$ 2,270,279
Original issue discount	(18,584)	(18,390)
Deferred financing costs	(15,882)	(21,403)
Total debt, net of original issue discount and deferred financing costs	2,113,957	2,230,486
Less: current portion	(7,237)	(45,166)
Total long-term debt, excluding current portion	2,106,720	2,185,320
Term Loan Facility
Debt Instrument [Line Items]
Original issue discount				$ (756)
Deferred financing costs				$ (564)
Term Loan | Term Loan Facility | USD
Debt Instrument [Line Items]
Total debt	0	916,153
Term Loan | Term Loan Facility | Euro
Debt Instrument [Line Items]
Total debt	0	335,808
Term Loan | New Term Loan Facility
Debt Instrument [Line Items]
Total debt	1,157,498	0
Senior Notes | 6.75% Senior Secured Notes due 2022
Debt Instrument [Line Items]
Total debt	$ 625,000	625,000
Debt instrument stated interest rate	6.75%				6.75%
Unsecured Debt | 5.75% Senior Unsecured Notes due 2025
Debt Instrument [Line Items]
Total debt	$ 300,000	300,000
Debt instrument stated interest rate	5.75%		5.75%
Line of Credit | ABL Facility
Debt Instrument [Line Items]
Total debt		25,000
Other
Debt Instrument [Line Items]
Total debt	$ 65,925	$ 68,318

Long-term Debt - Other Narrativ

Long-term Debt - Other Narratives (Details)

Dec. 11, 2017USD ($)

Oct. 03, 2017USD ($)

Jun. 22, 2017USD ($)

Jun. 12, 2017EUR (€)tranche

Dec. 29, 2016USD ($)

Nov. 14, 2016USD ($)

May 17, 2016USD ($)

May 04, 2016USD ($)

Oct. 24, 2013USD ($)

Dec. 31, 2018USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Dec. 31, 2018JPY (¥)

May 04, 2016EUR (€)

Dec. 31, 2014USD ($)

Debt Instrument [Line Items]

Long term debt outstanding

$ 2,148,423,000

$ 2,270,279,000

Debt extinguishment costs

0

47,875,000

$ 0

Deferred financing costs

15,882,000

21,403,000

Original issue discount

18,584,000

18,390,000

Fair value aggregate differences

$ 2,010,023,000

2,236,280,000

Debt covenant, net debt to EBITDA ratio, first three years

3

3

Debt covenant, net debt to EBITDA ratio, after three years

2.5

2.5

Foreign debt

Debt Instrument [Line Items]

Notes payable

$ 2,358,000

2,306,000

Maximum borrowing capacity

2,358,000

¥ 260,000,000

Term Loan Facility

Debt Instrument [Line Items]

Debt extinguishment costs

$ 474,000

Deferred financing costs

564,000

Original issue discount

$ 756,000

Previously Outstanding Debt

Debt Instrument [Line Items]

Debt extinguishment costs

$ 4,747,000

Deferred financing costs

6,252,000

Original issue discount

989,000

October 2013 NMTC Agreement | Chase

Debt Instrument [Line Items]

Proceeds from contributions from affiliates

$ 6,634,000

October 2013 NMTC Agreement | Potters Industries, LLC

Debt Instrument [Line Items]

Proceeds from contributions from affiliates

15,632,000

Notes payable

21,000,000

21,000,000

October 2013 NMTC Agreement | Potters Industries, LLC | Note payable I

Debt Instrument [Line Items]

Notes payable

5,368,000

October 2013 NMTC Agreement | Potters Industries, LLC | Notes payable II

Debt Instrument [Line Items]

Notes payable

$ 15,632,000

May 2016 NMTC Agreement | Potters Industries, LLC

Debt Instrument [Line Items]

Proceeds from contributions from affiliates

$ 7,822,000

Notes payable

11,000,000

11,000,000

May 2016 NMTC Agreement | Potters Industries, LLC | Note payable I

Debt Instrument [Line Items]

Notes payable

7,823,000

May 2016 NMTC Agreement | Potters Industries, LLC | Notes payable II

Debt Instrument [Line Items]

Notes payable

1,311,000

May 2016 NMTC Agreement | Potters Industries, LLC | Notes payable III

Debt Instrument [Line Items]

Notes payable

1,866,000

May 2016 NMTC Agreement | USB Investment Fund

Debt Instrument [Line Items]

Proceeds from contributions from affiliates

$ 3,732,000

Debt instrument, term

7 years

December 2016 NMTC Agreement | Potters Industries, LLC

Debt Instrument [Line Items]

Proceeds from contributions from affiliates

$ 7,775,000

Notes payable

11,000,000

11,000,000

December 2016 NMTC Agreement | Potters Industries, LLC | Note payable I

Debt Instrument [Line Items]

Notes payable

7,775,000

December 2016 NMTC Agreement | Potters Industries, LLC | Notes payable II

Debt Instrument [Line Items]

Notes payable

1,402,000

December 2016 NMTC Agreement | Potters Industries, LLC | Notes payable III

Debt Instrument [Line Items]

Notes payable

1,823,000

December 2016 NMTC Agreement | USB Investment Fund

Debt Instrument [Line Items]

Proceeds from contributions from affiliates

$ 3,815,000

June 2017 NMTC Agreement | Potters Industries, LLC

Debt Instrument [Line Items]

Notes payable

$ 8,820,000

8,820,000

Maximum indemnification liability

24,649,000

June 2017 NMTC Agreement | USB Investment Fund

Debt Instrument [Line Items]

Proceeds from contributions from affiliates

3,054,000

Notes payable

6,221,000

June 2017 NMTC Agreement | Community Reinvestment Fund, Inc.

Debt Instrument [Line Items]

Proceeds from contributions from affiliates

$ 9,000,000

Debt instrument, term

7 years

Term Loan | Term Loan Facility

Debt Instrument [Line Items]

Debt instrument face amount

$ 1,200,000,000

Term Loan | Term Loan Facility | EURIBOR

Debt Instrument [Line Items]

Variable rate on spread

4.75%

Term Loan | Term Loan Facility | USD

Debt Instrument [Line Items]

Debt instrument face amount

$ 900,000,000

Long term debt outstanding

0

916,153,000

Term Loan | Term Loan Facility | Euro

Debt Instrument [Line Items]

Debt instrument face amount

300,000,000

€ 265,000,000

Long term debt outstanding

0

335,808,000

Unsecured Debt | Floating Rate Senior Unsecured Notes due 2022

Debt Instrument [Line Items]

Debt instrument face amount

525,000,000

Long term debt outstanding

$ 78,792,000

Debt extinguishment costs

$ 6,043,000

32,284,000

Deferred financing costs

108,000

696,000

Original issue discount

1,176,000

$ 7,555,000

Senior Notes | 6.75% Senior Secured Notes due 2022

Debt Instrument [Line Items]

Debt instrument face amount

$ 625,000,000

Long term debt outstanding

$ 625,000,000

$ 625,000,000

Debt instrument stated interest rate

6.75%

6.75%

6.75%

6.75%

Senior Notes | 8.5% Senior Notes due 2022

Debt Instrument [Line Items]

Debt instrument face amount

$ 200,000,000

Debt extinguishment costs

7,996,000

Deferred financing costs

$ 5,207,000

Debt instrument stated interest rate

8.50%

8.50%

8.50%

Line of Credit | Belfius Bank NV

Debt Instrument [Line Items]

Maximum borrowing capacity | €

€ 14,500,000

Number of tranches | tranche

4

Line of Credit | Euro Roll-over Line of Credit Maturing December 2021 | Belfius Bank NV

Debt Instrument [Line Items]

Line of credit outstanding

$ 5,148,000

Debt instrument stated interest rate

1.10%

1.10%

Maximum borrowing capacity | €

€ 7,500,000

Periodic principal payment | €

€ 750,000

Line of Credit | Euro Roll-over Line of Credit Maturing December 2021 | Belfius Bank NV | EURIBOR | Minimum

Debt Instrument [Line Items]

Variable rate on spread

1.10%

Line of Credit | Euro Roll-over Line of Credit Maturing December 2021 | Belfius Bank NV | EURIBOR | Maximum

Debt Instrument [Line Items]

Variable rate on spread

1.55%

Line of Credit | Euro Roll-over Line of Credit Maturing September 2022 | Belfius Bank NV

Debt Instrument [Line Items]

Line of credit outstanding

$ 3,433,000

Debt instrument stated interest rate

1.85%

1.85%

Maximum borrowing capacity | €

€ 3,000,000

Line of Credit | Euro Roll-over Line of Credit Maturing September 2022 | Belfius Bank NV | EURIBOR | Minimum

Debt Instrument [Line Items]

Variable rate on spread

1.85%

Line of Credit | Euro Roll-over Line of Credit Maturing September 2022 | Belfius Bank NV | EURIBOR | Maximum

Debt Instrument [Line Items]

Variable rate on spread

2.15%

Line of Credit | Working Capital | Belfius Bank NV

Debt Instrument [Line Items]

Line of credit outstanding

$ 1,945,000

Debt instrument stated interest rate

0.90%

0.90%

Maximum borrowing capacity | €

€ 3,000,000

Line of Credit | Working Capital | Belfius Bank NV | EURIBOR | Minimum

Debt Instrument [Line Items]

Variable rate on spread

0.90%

Line of Credit | Working Capital | Belfius Bank NV | EURIBOR | Maximum

Debt Instrument [Line Items]

Variable rate on spread

1.20%

Line of Credit | CAPEX Line | Belfius Bank NV

Debt Instrument [Line Items]

Line of credit outstanding

$ 1,144,000

Debt instrument stated interest rate

1.25%

1.25%

Maximum borrowing capacity | €

€ 1,000,000

Line of Credit | CAPEX Line | Belfius Bank NV | EURIBOR | Minimum

Debt Instrument [Line Items]

Variable rate on spread

1.25%

Line of Credit | CAPEX Line | Belfius Bank NV | EURIBOR | Maximum

Debt Instrument [Line Items]

Variable rate on spread

1.80%

Long-term Debt - Term Loans and

Long-term Debt - Term Loans and ABL Facility Narrative (Details)	Aug. 07, 2017USD ($)	Nov. 14, 2016USD ($)	May 04, 2016USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Aug. 07, 2017EUR (€)	Nov. 14, 2016EUR (€)	May 04, 2016EUR (€)
Debt Instrument [Line Items]
New financing costs				$ 0	$ 47,875,000	$ 0
Unamortized deferred financing costs				15,882,000	21,403,000
Original issue discount				18,584,000	18,390,000
Long term debt outstanding				2,148,423,000	2,270,279,000
Debt covenant, fixed-charge coverage ratio minimum			1						1
Term Loan Facility
Debt Instrument [Line Items]
Debt instrument issued, percentage of principal			99.00%						99.00%
New financing costs		$ 474,000
Unamortized deferred financing costs		564,000
Original issue discount		756,000
First Amendment
Debt Instrument [Line Items]
New financing costs	$ 199,000
Unamortized deferred financing costs	105,000
Original issue discount	162,000
Term Loan | Term Loan Facility
Debt Instrument [Line Items]
Debt instrument face amount			$ 1,200,000,000
Scheduled quarterly principal payments			0.25%						0.25%
Term Loan | Term Loan Facility | LIBOR
Debt Instrument [Line Items]
Debt instrument, interest rate floor			1.00%
Term Loan | Term Loan Facility | EURIBOR
Debt Instrument [Line Items]
Variable rate on spread			4.75%
Term Loan | Term Loan Facility | Base Rate
Debt Instrument [Line Items]
Variable rate on spread			3.75%
Debt instrument, interest rate floor			2.00%
USD | Term Loan | Term Loan Facility
Debt Instrument [Line Items]
Debt instrument face amount			$ 900,000,000
Long term debt outstanding				0	916,153,000
USD | Term Loan | First Amendment
Debt Instrument [Line Items]
Debt instrument face amount	$ 927,750,000	927,750,000
Additional borrowings		$ 30,000,000
USD | Term Loan | First Amendment | LIBOR
Debt Instrument [Line Items]
Variable rate on spread	3.25%	4.25%
Debt instrument, interest rate floor	0.00%
Euro | Term Loan | Term Loan Facility
Debt Instrument [Line Items]
Debt instrument face amount			300,000,000						€ 265,000,000
Long term debt outstanding				0	335,808,000
Euro | Term Loan | First Amendment
Debt Instrument [Line Items]
Debt instrument face amount | €							€ 283,338,000	€ 283,338,000
Additional borrowings | €								€ 19,000,000
Euro | Term Loan | First Amendment | LIBOR
Debt Instrument [Line Items]
Variable rate on spread		4.00%
Euro | Term Loan | First Amendment | EURIBOR
Debt Instrument [Line Items]
Variable rate on spread	3.25%
Debt instrument, interest rate floor	0.75%
Euro | Term Loan | First Amendment | Base Rate
Debt Instrument [Line Items]
Variable rate on spread		3.25%
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Long term debt outstanding					$ 25,000,000
Revolving Credit Facility | Line of Credit | ABL Facility
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 200,000,000
Commitment fee percentage			0.375%
Potential commitment fee percentage			0.25%
Long term debt outstanding				0
Letters of credit outstanding				$ 19,796,000
Revolving Credit Facility | Line of Credit | ABL Facility | LIBOR | Minimum
Debt Instrument [Line Items]
Variable rate on spread			1.50%
Revolving Credit Facility | Line of Credit | ABL Facility | LIBOR | Maximum
Debt Instrument [Line Items]
Variable rate on spread			2.00%
Revolving Credit Facility | Line of Credit | ABL Facility | Base Rate | Minimum
Debt Instrument [Line Items]
Variable rate on spread			0.50%
Revolving Credit Facility | Line of Credit | ABL Facility | Base Rate | Maximum
Debt Instrument [Line Items]
Variable rate on spread			1.00%
Revolving Credit Facility | USD | Line of Credit | ABL Facility
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 150,000,000
Revolving Credit Facility | Canada, Dollars | Line of Credit | ABL Facility
Debt Instrument [Line Items]
Maximum borrowing capacity			10,000,000
Revolving Credit Facility | Euro | Line of Credit | ABL Facility
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 40,000,000

Long-term Debt - Notes (Details

Long-term Debt - Notes (Details) - USD ($)	Dec. 11, 2017	Oct. 03, 2017	May 04, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014
Debt Instrument [Line Items]
Long term debt outstanding				$ 2,148,423,000	$ 2,270,279,000
Debt extinguishment costs				0	47,875,000	$ 0
Unamortized deferred financing costs				15,882,000	21,403,000
Original issue discount				18,584,000	18,390,000
Repayments of long-term debt				$ 1,369,690,000	739,472,000	$ 479,059,000
Senior Notes | 6.75% Senior Secured Notes due 2022
Debt Instrument [Line Items]
Debt instrument face amount			$ 625,000,000
Debt instrument stated interest rate			6.75%	6.75%
Long term debt outstanding				$ 625,000,000	625,000,000
Senior Notes | 8.5% Senior Notes due 2022
Debt Instrument [Line Items]
Debt instrument face amount							$ 200,000,000
Debt instrument stated interest rate				8.50%			8.50%
Redemption premium paid	$ 8,500,000
Debt instrument issued, percentage of principal							100.00%
Debt extinguishment costs	7,996,000
Unamortized deferred financing costs	5,207,000
Repayments of long-term debt	200,000,000
Unsecured Debt | Floating Rate Senior Unsecured Notes due 2022
Debt Instrument [Line Items]
Debt instrument face amount			$ 525,000,000
Redemption premium paid	7,091,000
Debt instrument issued, percentage of principal			98.00%
Long term debt outstanding		$ 78,792,000
Debt extinguishment amount	78,792,000	446,208,000
Debt extinguishment costs	6,043,000	32,284,000
Unamortized deferred financing costs	108,000	696,000
Original issue discount	1,176,000	$ 7,555,000
Unsecured Debt | Floating Rate Senior Unsecured Notes due 2022 | LIBOR
Debt Instrument [Line Items]
Variable rate on spread			10.75%
Debt instrument, interest rate floor			1.00%
Unsecured Debt | 5.75% Senior Unsecured Notes due 2025
Debt Instrument [Line Items]
Debt instrument face amount	$ 300,000,000
Debt instrument stated interest rate	5.75%			5.75%
Debt instrument, redemption price percentage	105.75%			100.00%
Long term debt outstanding				$ 300,000,000	$ 300,000,000
Debt instrument, call premium	1.00%
Unsecured Debt | 5.75% Senior Unsecured Notes due 2025 | U.S. Treasury
Debt Instrument [Line Items]
Variable rate on spread	5.00%
Change of Control | Senior Notes | 6.75% Senior Secured Notes due 2022
Debt Instrument [Line Items]
Debt instrument, redemption price percentage				101.00%
Change of Control | Unsecured Debt | 5.75% Senior Unsecured Notes due 2025
Debt Instrument [Line Items]
Debt instrument, redemption price percentage				101.00%
Minimum | Event of Default | Unsecured Debt | 5.75% Senior Unsecured Notes due 2025
Debt Instrument [Line Items]
Potential percentage of principal redeemed					30.00%
Maximum | Exercise of Call Option | Unsecured Debt | 5.75% Senior Unsecured Notes due 2025
Debt Instrument [Line Items]
Potential percentage of principal redeemed	40.00%

Long-term Debt - Senior Credit

Long-term Debt - Senior Credit Facilities (Details) € in Thousands	Feb. 08, 2018USD ($)	May 04, 2016USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2017USD ($)	Nov. 14, 2016USD ($)
Debt Instrument [Line Items]
Original issue discount			$ 18,584,000				$ 18,390,000
Term Loan Facility
Debt Instrument [Line Items]
Debt instrument issued, percentage of principal		99.00%
Original issue discount								$ 756,000
Term Loan | New Term Loan Facility
Debt Instrument [Line Items]
Debt prepayments			55,000,000	$ 45,000,000
Scheduled quarterly principal payments	0.25%
Debt instrument face amount	$ 1,267,000,000
Write off of deferred financing costs			301,000	258,000
Write-off of original issue discount			707,000	$ 606,000
Term Loan | New Term Loan Facility | LIBOR
Debt Instrument [Line Items]
Variable rate on spread	2.50%
Term Loan | Term Loan Facility
Debt Instrument [Line Items]
Debt extinguishment costs	$ 2,124,000
Scheduled quarterly principal payments		0.25%
Debt instrument face amount		$ 1,200,000,000
Write off of deferred financing costs	1,403,000
Write-off of original issue discount	$ 2,352,000
Term Loan | Term Loan Facility | EURIBOR
Debt Instrument [Line Items]
Variable rate on spread		4.75%
Revolving Credit Facility | Line of Credit | Senior Secured Credit Facilities
Debt Instrument [Line Items]
Repayments of lines of credit					$ 12,000,000
Cross currency swap
Debt Instrument [Line Items]
Derivative, notional amount			$ 320,404,000			€ 280,000

Long-term Debt - Redemption Rat

Long-term Debt - Redemption Rate (Details)	Dec. 11, 2017	Dec. 31, 2018
Senior Notes | 6.75% Senior Secured Notes due 2022 | Debt Instrument, Redemption, Period One
Debt Instrument, Redemption
Debt instrument, redemption price percentage		103.375%
Senior Notes | 6.75% Senior Secured Notes due 2022 | Debt Instrument, Redemption, Period Two
Debt Instrument, Redemption
Debt instrument, redemption price percentage		101.688%
Senior Notes | 6.75% Senior Secured Notes due 2022 | Debt Instrument, Redemption, Period Three
Debt Instrument, Redemption
Debt instrument, redemption price percentage		100.00%
Unsecured Debt | 5.75% Senior Unsecured Notes due 2025
Debt Instrument, Redemption
Debt instrument, redemption price percentage	105.75%	100.00%
Unsecured Debt | 5.75% Senior Unsecured Notes due 2025 | Debt Instrument, Redemption, Period One
Debt Instrument, Redemption
Debt instrument, redemption price percentage		102.875%
Unsecured Debt | 5.75% Senior Unsecured Notes due 2025 | Debt Instrument, Redemption, Period Two
Debt Instrument, Redemption
Debt instrument, redemption price percentage		101.438%
Unsecured Debt | 5.75% Senior Unsecured Notes due 2025 | Debt Instrument, Redemption, Period Three
Debt Instrument, Redemption
Debt instrument, redemption price percentage		100.00%

Long-term Debt - Debt Maturity

Long-term Debt - Debt Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Long-term Debt, Fiscal Year Maturity
2,019	$ 7,237
2,020	1,718
2,021	1,717
2,022	628,433
2,023	3,689
Thereafter	1,505,629
Total debt	$ 2,148,423	$ 2,270,279

Other Long-term Liabilities (De

Other Long-term Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Pension benefits	$ 75,430	$ 69,914
Supply contract (see Note 25)	0	20,612
Other postretirement benefits	3,233	4,051
Supplemental retirement plans	10,763	11,667
Reserve for uncertain tax positions	3,176	4,244
Asset retirement obligation	4,224	4,094
Other	7,999	5,889
Total	$ 104,825	$ 120,471

Financial Instruments - Narrati

Financial Instruments - Narratives (Details) € in Thousands, MMBTU in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2016USD ($)	Dec. 31, 2018USD ($)MMBTU	Dec. 31, 2018EUR (€)	Nov. 13, 2018USD ($)
Derivative [Line Items]
Derivative, notional quantity (in MMBTU) | MMBTU		3.9
Amount of derivative loss expected to be transfered from OCI		$ 640,000
Cross currency swap
Derivative [Line Items]
Derivative, notional amount		$ 320,404,000	€ 280,000
Interest rate caps
Derivative [Line Items]
Premium paid to acquire derivative instrument	$ 1,551,000
Derivative, cap interest rate		2.50%	2.50%
Derivative, notional amount	$ 1,000,000,000
Interest rate caps | Minimum
Derivative [Line Items]
Derivative, cap interest rate	1.50%
Interest rate caps | Maximum
Derivative [Line Items]
Derivative, cap interest rate	3.00%
Interest rate cap II
Derivative [Line Items]
Derivative, cap interest rate				3.50%
Derivative, notional amount				$ 500,000

Financial Instruments - Fair Va

Financial Instruments - Fair Value (Details) - Derivatives designated as cash flow hedges: - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivative assets:
Total derivative assets	$ 20,768	$ 1,043
Cash Flow Hedging
Derivative assets:
Total derivative assets	1,925	1,043
Liability derivatives:
Total derivative liabilities	2,026	448
Cash Flow Hedging | Natural gas swaps | Prepaid and other current assets
Derivative assets:
Total derivative assets	21	0
Cash Flow Hedging | Natural gas swaps | Accrued liabilities
Liability derivatives:
Total derivative liabilities	36	318
Cash Flow Hedging | Natural gas swaps | Other long-term liabilities
Liability derivatives:
Total derivative liabilities	148	130
Cash Flow Hedging | Interest rate caps | Prepaid and other current assets
Derivative assets:
Total derivative assets	1,358	44
Cash Flow Hedging | Interest rate caps | Other long-term assets
Derivative assets:
Total derivative assets	546	999
Cash Flow Hedging | Interest rate caps | Other long-term liabilities
Liability derivatives:
Total derivative liabilities	1,842	0
Net Investment Hedging
Derivative assets:
Total derivative assets	18,843	0
Net Investment Hedging | Cross currency swap | Prepaid and other current assets
Derivative assets:
Total derivative assets	5,499	0
Net Investment Hedging | Cross currency swap | Other long-term assets
Derivative assets:
Total derivative assets	$ 13,344	$ 0

Financial Instruments - Effect

Financial Instruments - Effect on Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in OCI on derivatives	$ (344)	$ (6,060)	$ 3,448
Amount of gain (loss) reclassified from accumulated OCI into income	97	(262)	(1,433)
Interest rate caps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in OCI on derivatives	(981)	(4,760)	4,250
Interest rate caps | Interest expense
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) reclassified from accumulated OCI into income	(256)	(40)	0
Natural gas swaps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in OCI on derivatives	637	(1,300)	(802)
Natural gas swaps | Cost of goods sold
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) reclassified from accumulated OCI into income	$ 353	$ (222)	$ (1,433)

Financial Instruments - Cash Fl

Financial Instruments - Cash Flow Hedge Impact on Statement of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Cost of goods sold	$ (1,226,520)	$ (1,095,265)	$ (810,085)
Interest (expense) income	(113,723)	(179,044)	(140,315)
Gain (loss) on cash flow hedging relationships: | Amount of gain (loss) reclassified from AOCI into income | Interest rate caps
Derivative [Line Items]
Cost of goods sold	0	0	0
Interest (expense) income	(256)	(40)	0
Gain (loss) on cash flow hedging relationships: | Amount of gain (loss) reclassified from AOCI into income | Natural gas swaps
Derivative [Line Items]
Cost of goods sold	353	(222)	(1,433)
Interest (expense) income	$ 0	$ 0	$ 0

Financial Instruments - Net Inv

Financial Instruments - Net Investment Hedge Impact on AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cross currency swap
Derivative [Line Items]
Amount of gain (loss) recognized in OCI on derivative	$ 18,843	$ 0	$ 0
(Gain) loss on sale of subsidiary
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	0	0	0
Interest (expense) income
Derivative [Line Items]
Amount of gain (loss) recognized in income on derivative (amount excluded from effectiveness testing)	$ 7,898	$ 0	$ 0

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Domestic	$ 3,935	$ (137,147)	$ (84,094)
Foreign	84,681	76,513	14,977
Income (loss) before income taxes and noncontrolling interest	$ 88,616	$ (60,634)	$ (69,117)

Income Taxes - Narratives (Deta

Income Taxes - Narratives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards
Transition tax measurement period adjustment	$ (2,102)
Valuation allowance, deferred tax asset, increase (decrease)	$ (20,038)	$ 20,753
Tax at statutory rate	21.00%
Impact to income tax expense from GILTI	$ 15,444
Effective income tax rate			35.00%
Provision (benefit) for income taxes	28,995	(119,197)	$ 10,041
Change in tax status-Eco Services-Passthrough to C-Corporation	$ 0	0	$ 33,891
Federal statutory income tax rate, former rate, percent	35.00%
Net deferred tax liability	$ 177,329	187,036
Deferred tax asset non-current	18,795	2,300
Deferred income taxes	196,124	189,336
Unremitted and no invested earnings from non- U.S subsidiaries and affiliates	168,304	210,979
Unrecognized tax benefit that would impact effective tax rate	10,175	11,431
Interest and penalties from unrecognized tax positions	42	52
Accrued penalties and interest	1,088	1,270
Operating loss carryforward	131,453
Net operating loss carryforwards	116,607	144,267
163(j) interest disallowance	57,705
Federal
Operating Loss Carryforwards
Operating loss carryforward	284,237
Federal | Tax Years Prior to 2014 Change in Control
Operating Loss Carryforwards
Operating loss carryforward	144,357
Federal | Tax Years After 2014 Change in Control
Operating Loss Carryforwards
Operating loss carryforward	139,880
State and local
Operating Loss Carryforwards
Operating loss carryforward	681,010
Operating loss carryforward, valuation allowance	17,718
Net operating loss carryforwards	33,179
Operating loss carryforward, net of valuation allowance	15,461
State and local | Tax Year 2018
Operating Loss Carryforwards
Operating loss carryforward	21,594
Foreign
Operating Loss Carryforwards
Operating loss carryforward, valuation allowance	11,940
Net operating loss carryforwards	31,431
Operating loss carryforward, net of valuation allowance	19,491
Foreign | Tax Year 2019
Operating Loss Carryforwards
Operating carryforward subject to expiration	586
Foreign | Tax Year 2028
Operating Loss Carryforwards
Operating carryforward subject to expiration	92
Foreign | Tax Year 2029
Operating Loss Carryforwards
Operating carryforward subject to expiration	7,616
Foreign | Indefinite
Operating Loss Carryforwards
Operating carryforward not subject to expiration	120,954
Potters
Operating Loss Carryforwards
Net deferred tax liability	$ 45,251	$ 45,873

Income Taxes - Provision for In

Income Taxes - Provision for Income Tax (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 0	$ 0	$ 0
State	2,470	806	91
Foreign	23,080	20,209	10,088
Current income tax	25,550	21,015	10,179
Deferred:
Federal	12,854	(135,970)	8,654
State	(784)	(1,817)	292
Foreign	(8,625)	(2,425)	(9,084)
Deferred income tax	3,445	(140,212)	(138)
Total	$ 28,995	$ (119,197)	$ 10,041

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Asset (Liability) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 116,607	$ 144,267
Section 163j interest disallowance carryforward	13,387	0
Pension	16,397	16,255
Post retirement health	1,385	561
Transaction costs	708	1,183
Natural gas contracts and interest rate swaps	335	225
Unrealized translation losses	3,737	5,065
US research and development credits	1,173	0
Other	38,855	38,290
Valuation allowance	(48,711)	(64,945)
Deferred tax asset net of valuation	143,873	140,901
Deferred tax liabilities:
Depreciation	(92,911)	(86,532)
Undistributed earnings of non-US subsidiaries	(6,648)	(8,334)
Inventory	(10,432)	(11,324)
Intangible assets	(174,327)	(184,937)
Natural gas contracts	(4,654)	0
Other	(32,230)	(36,810)
Deferred tax liability	(321,202)	(327,937)
Deferred Tax Liabilities, Net	$ (177,329)	$ (187,036)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Statutory Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Tax at statutory rate	$ 18,610	$ (21,222)	$ (24,191)
State income taxes, net of federal income tax benefit	1,203	(7,754)	(4,110)
Repatriation of non-US earnings	14,187	(24,912)	4,576
Change in tax status-Eco Services-Passthrough to C-Corporation	0	0	33,891
Changes in uncertain tax positions	(996)	974	(2,383)
Change in valuation allowances	5,075	6,771	2,577
Rate changes	(4,016)	(63,319)	0
Change in state effective rates	691	(340)	(290)
Foreign withholding taxes	1,828	978	1,505
Foreign tax rate differential	2,191	(13,634)	(3,040)
Non-deductible transaction costs	84	1,679	667
Permanent difference created by foreign exchange gain or loss	(7,550)	3,503	1,686
Research and development tax credits	(1,173)	0	0
Other, net	(1,139)	(1,921)	(847)
Total	$ 28,995	$ (119,197)	$ 10,041

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Asset Valuation Rolforward (Details) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Movement in Valuation Allowances and Reserves
Beginning Balance	$ 64,945	$ 38,271
Additions	5,314	34,863
Reductions	(21,548)	(8,189)
Ending Balance	48,711	$ 64,945
Net change in period	$ (16,234)

Income Taxes - Change in Unreco

Income Taxes - Change in Unrecognized Tax Position (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Balance at beginning of period	$ 11,431	$ 16,128
Increases related to prior year tax positions	0	68
Decreases related to prior year tax positions	(1,538)	(5,508)
Increases related to current year tax positions	282	743
Balance at end of period	$ 10,175	$ 11,431

Income Taxes - Payment for Taxe

Income Taxes - Payment for Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards
Cash paid for taxes	$ 23,842	$ 29,199	$ 16,981
Domestic
Operating Loss Carryforwards
Cash paid for taxes	2,160	1,647	373
Foreign
Operating Loss Carryforwards
Cash paid for taxes	$ 21,682	$ 27,552	$ 16,608

Benefit Plans - Change in Benef

Benefit Plans - Change in Benefit Obligation and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Pension Plans
Defined Benefit Plan, Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of period	$ 314,892
Fair value of plan assets at end of the period	287,542	$ 314,892
Defined Benefit Pension Plans | U.S.
Defined Benefit Plan, Change in Benefit Obligation
Benefit obligation at beginning of period	261,102	247,418
Service cost	1,019	1,219	$ 2,130
Interest cost	9,599	10,115	7,680
Participant contributions	0	0
Plan amendments	0	0
Plan curtailments	(952)	0
Plan settlements	0	(2,264)
Benefits paid	(11,453)	(9,591)
Expenses paid	0	0
Net transfer in	0	0
Actuarial (gains) losses	(13,004)	14,205
Translation adjustment	0	0
Benefit obligation at end of the period	246,311	261,102	247,418
Defined Benefit Plan, Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of period	218,374	198,915
Actual return on plan assets	(12,854)	27,554
Employer contributions	1,688	3,760
Employee contributions	0	0
Plan settlements	0	(2,264)
Benefits paid	(11,453)	(9,591)
Expenses paid	0	0
Acquisitions	0	0
Translation adjustment	0	0
Fair value of plan assets at end of the period	195,755	218,374	198,915
Funded status of the plans (underfunded)	(50,556)	(42,728)
Defined Benefit Pension Plans | Foreign
Defined Benefit Plan, Change in Benefit Obligation
Benefit obligation at beginning of period	119,710	106,025
Service cost	3,566	3,686	2,106
Interest cost	3,340	3,271	2,224
Participant contributions	570	493
Plan amendments	179	0
Plan curtailments	(340)	0
Plan settlements	(1,071)	0
Benefits paid	(2,569)	(2,967)
Expenses paid	(363)	(319)
Net transfer in	1,535	0
Actuarial (gains) losses	(5,432)	(2,169)
Translation adjustment	(7,022)	11,690
Benefit obligation at end of the period	112,103	119,710	106,025
Defined Benefit Plan, Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of period	96,518	86,145
Actual return on plan assets	(540)	217
Employer contributions	4,249	3,781
Employee contributions	570	493
Plan settlements	(1,071)	0
Benefits paid	(2,569)	(2,967)
Expenses paid	(363)	(319)
Acquisitions	1,013	0
Translation adjustment	(6,020)	9,168
Fair value of plan assets at end of the period	91,787	96,518	86,145
Funded status of the plans (underfunded)	(20,316)	(23,192)
Supplemental Retirement Plans
Defined Benefit Plan, Change in Benefit Obligation
Benefit obligation at beginning of period	12,781	13,225
Interest cost	450	489	328
Benefits paid	(1,070)	(1,179)
Actuarial (gains) losses	(293)	246
Benefit obligation at end of the period	11,868	12,781	13,225
Defined Benefit Plan, Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of period	0	0
Employer contributions	1,070	1,179
Benefits paid	(1,070)	(1,179)
Fair value of plan assets at end of the period	0	0	0
Funded status of the plans (underfunded)	(11,868)	(12,781)
Other Postretirement Benefits Plans
Defined Benefit Plan, Change in Benefit Obligation
Benefit obligation at beginning of period	4,612	4,620
Service cost	16	21	37
Interest cost	150	174	151
Participant contributions	251	251
Plan amendments	(271)	0
Benefits paid	(1,061)	(923)
Medical subsidies received	74	0
Premiums paid	66	3
Actuarial (gains) losses	172	418
Translation adjustment	(63)	54
Benefit obligation at end of the period	3,814	4,612	4,620
Defined Benefit Plan, Change in Fair Value of Plan Assets
Fair value of plan assets at beginning of period	0	0
Employer contributions	802	675
Employee contributions	251	251
Benefits paid	(1,061)	(923)
Medical subsidies received	74	0
Premiums paid	66	3
Fair value of plan assets at end of the period	0	0	$ 0
Funded status of the plans (underfunded)	$ (3,814)	$ (4,612)

Benefit Plans - Recognized on t

Benefit Plans - Recognized on the Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Pension Plans | U.S.
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position
Noncurrent asset	$ 0	$ 0
Current liability	0	0
Noncurrent liability	(50,556)	(42,728)
Accumulated other comprehensive income (loss)	1,218	10,499
Net amount recognized	(49,338)	(32,229)
Defined Benefit Pension Plans | Foreign
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position
Noncurrent asset	4,670	3,503
Current liability	(748)	(673)
Noncurrent liability	(24,238)	(26,022)
Accumulated other comprehensive income (loss)	(1,829)	(2,871)
Net amount recognized	(22,145)	(26,063)
Supplemental Retirement Plans
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position
Current liability	(1,105)	(1,115)
Noncurrent liability	(10,763)	(11,667)
Accumulated other comprehensive income (loss)	795	573
Net amount recognized	(11,073)	(12,209)
Other Postretirement Benefits Plans
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position
Current liability	(581)	(561)
Noncurrent liability	(3,233)	(4,051)
Accumulated other comprehensive income (loss)	830	885
Net amount recognized	$ (2,984)	$ (3,727)

Benefit Plans - Accumulated Oth

Benefit Plans - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Pension Plans | U.S.
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax
Prior service credit	$ 0	$ 0
Net gain (loss)	1,618	13,943
Gross amount recognized	1,618	13,943
Deferred income taxes	(400)	(3,444)
Net amount recognized	1,218	10,499
Defined Benefit Pension Plans | Foreign
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax
Prior service credit	(170)	0
Net gain (loss)	(2,133)	(3,923)
Gross amount recognized	(2,303)	(3,923)
Deferred income taxes	474	1,052
Net amount recognized	(1,829)	(2,871)
Supplemental Retirement Plans
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax
Net gain (loss)	1,055	761
Gross amount recognized	1,055	761
Deferred income taxes	(260)	(188)
Net amount recognized	795	573
Other Postretirement Benefits Plans
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax
Prior service credit	525	366
Net gain (loss)	500	719
Gross amount recognized	1,025	1,085
Deferred income taxes	(195)	(200)
Net amount recognized	$ 830	$ 885

Benefit Plans - Net Periodic Pe

Benefit Plans - Net Periodic Pension Expense Benefit (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Pension Plans | U.S.
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	$ 1,019,000	$ 1,219,000	$ 2,130,000
Interest cost	9,599,000	10,115,000	7,680,000
Expected return on plan assets	(12,851,000)	(12,277,000)	(9,293,000)
Amortization of net gain	0	0	0
Curtailment gain recognized	(576,000)	0	(1,311,000)
Settlement (gain) loss recognized	0	(48,000)	152,000
Net periodic expense (benefit)	(2,809,000)	(991,000)	(642,000)
Defined Benefit Pension Plans | Foreign
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	3,566,000	3,686,000	2,106,000
Interest cost	3,340,000	3,271,000	2,224,000
Expected return on plan assets	(3,311,000)	(3,208,000)	(2,038,000)
Amortization of net gain	49,000	(9,000)	(10,000)
Curtailment gain recognized	(340,000)	0	(517,000)
Settlement (gain) loss recognized	(11,000)	0	0
Net periodic expense (benefit)	3,293,000	3,740,000	1,765,000
Supplemental Retirement Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Interest cost	450,000	489,000	328,000
Net periodic expense (benefit)	450,000	489,000	328,000
Estimated amortization of actuarial gain for next fiscal period	0
Other Postretirement Benefits Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	16,000	21,000	37,000
Interest cost	150,000	174,000	151,000
Amortization of prior service credit	(112,000)	(78,000)	0
Amortization of net gain	(26,000)	(45,000)	(17,000)
Net periodic expense (benefit)	28,000	$ 72,000	$ 171,000
Estimated amortization of actuarial gain for next fiscal period	32,000
Estimated amortization of prior service credit for next fiscal period	$ 130,000

Benefit Plans - Accumulated Ben

Benefit Plans - Accumulated Benefit Obligation (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Pension Plans | U.S.
Defined Benefit Plan Disclosure
Accumulated benefit obligation	$ 244,580	$ 257,882
Defined Benefit Plan, Funded (Unfunded) Status of Plan
Projected benefit obligation	246,311	261,102
Accumulated benefit obligation	244,580	257,882
Fair value of plan assets	195,755	218,374
Defined Benefit Pension Plans | Foreign
Defined Benefit Plan Disclosure
Accumulated benefit obligation	107,910	114,095
Defined Benefit Plan, Funded (Unfunded) Status of Plan
Projected benefit obligation	82,656	67,750
Accumulated benefit obligation	78,862	64,526
Fair value of plan assets	57,670	42,632
Supplemental Retirement Plans
Defined Benefit Plan Disclosure
Accumulated benefit obligation	$ 11,868	$ 12,781

Benefit Plans - Weighted Averag

Benefit Plans - Weighted Average Assumptions for Pension Obligation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Pension Plans | U.S.
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation
Discount rate	4.32%	3.74%
Rate of compensation increase	3.00%	3.00%
Defined Benefit Pension Plans | Foreign
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation
Discount rate	3.01%	2.91%
Rate of compensation increase	2.44%	2.57%
Supplemental Retirement Plans
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation
Discount rate	4.20%	3.60%
Rate of compensation increase	0.00%	0.00%
Other Postretirement Benefits Plans
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation
Discount rate	3.53%	3.74%
Immediate trend rate	6.59%	6.84%
Ultimate trend rate	4.50%	4.50%
Year that the rate reaches ultimate trend rate	2,035	2,035

Benefit Plans - Weighted Aver_2

Benefit Plans - Weighted Average Assumptions for Net Periodic Cost (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Pension Plans | U.S.
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost
Discount rate	3.74%	4.24%	4.02%
Rate of compensation increase	3.00%	3.00%	3.10%
Expected return on assets	6.00%	6.37%	6.34%
Defined Benefit Pension Plans | Foreign
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost
Discount rate	2.91%	2.99%	5.16%
Rate of compensation increase	2.57%	2.97%	3.95%
Expected return on assets	3.52%	3.58%	5.62%
Supplemental Retirement Plans
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost
Discount rate	3.60%	3.90%	3.40%
Rate of compensation increase	0.00%	0.00%	0.00%
Other Postretirement Benefits Plans
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost
Discount rate	3.53%	3.74%	3.92%

Benefit Plans - Plan Assets (De

Benefit Plans - Plan Assets (Details) - Defined Benefit Pension Plans - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 287,542	$ 314,892
U.S.
Defined Benefit Plan Disclosure
Fair value of plan assets	195,755	218,374	$ 198,915
Quoted Prices in Active Markets (Level 1)
Defined Benefit Plan Disclosure
Fair value of plan assets	195,949	158,790
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of plan assets	86,572	151,952
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of plan assets	5,021	4,150	$ 3,286
Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of plan assets	57,000	1,072
Cash and cash equivalents | U.S.
Defined Benefit Plan Disclosure
Fair value of plan assets	56
Cash and cash equivalents | Quoted Prices in Active Markets (Level 1)
Defined Benefit Plan Disclosure
Fair value of plan assets	56,925	934
Cash and cash equivalents | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of plan assets	75	138
Cash and cash equivalents | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 0	0
Equity Securities | PQ Corporation Retirement Plan | U.S.
Defined Benefit Plan Disclosure
Target asset plan allocation percentage	45.00%
Equity Securities | Eco Services Pension Equity Plan | U.S.
Defined Benefit Plan Disclosure
Target asset plan allocation percentage	40.00%
Equity Securities | Eco Services Hourly Pension Plan | U.S.
Defined Benefit Plan Disclosure
Target asset plan allocation percentage	45.00%
U.S. investment funds
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 35,103	56,309
U.S. investment funds | Quoted Prices in Active Markets (Level 1)
Defined Benefit Plan Disclosure
Fair value of plan assets	35,103	43,625
U.S. investment funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of plan assets	0	12,684
U.S. investment funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
International investment funds
Defined Benefit Plan Disclosure
Fair value of plan assets	44,508	70,308
International investment funds | Quoted Prices in Active Markets (Level 1)
Defined Benefit Plan Disclosure
Fair value of plan assets	24,040	28,827
International investment funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of plan assets	20,468	41,481
International investment funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 0	0
Fixed income securities | PQ Corporation Retirement Plan | U.S.
Defined Benefit Plan Disclosure
Target asset plan allocation percentage	55.00%
Fixed income securities | Eco Services Pension Equity Plan | U.S.
Defined Benefit Plan Disclosure
Target asset plan allocation percentage	60.00%
Fixed income securities | Eco Services Hourly Pension Plan | U.S.
Defined Benefit Plan Disclosure
Target asset plan allocation percentage	55.00%
Government securities
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 10,121	11,433
Government securities | Quoted Prices in Active Markets (Level 1)
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Government securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of plan assets	10,121	11,433
Government securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Corporate bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	77,229	82,585
Corporate bonds | Quoted Prices in Active Markets (Level 1)
Defined Benefit Plan Disclosure
Fair value of plan assets	72,216	77,685
Corporate bonds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of plan assets	5,013	4,900
Corporate bonds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Investment fund bonds
Defined Benefit Plan Disclosure
Fair value of plan assets	25,152	54,263
Investment fund bonds | Quoted Prices in Active Markets (Level 1)
Defined Benefit Plan Disclosure
Fair value of plan assets	7,665	7,719
Investment fund bonds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of plan assets	17,487	46,544
Investment fund bonds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Insurance contracts
Defined Benefit Plan Disclosure
Fair value of plan assets	38,429	38,922
Insurance contracts | Quoted Prices in Active Markets (Level 1)
Defined Benefit Plan Disclosure
Fair value of plan assets	0	0
Insurance contracts | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of plan assets	33,408	34,772
Insurance contracts | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of plan assets	$ 5,021	$ 4,150

Benefit Plans - Level 3 Rollfor

Benefit Plans - Level 3 Rollforward (Details) - Defined Benefit Pension Plans - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure
Fair value of plan assets at beginning of period	$ 314,892
Fair value of plan assets at end of the period	287,542	$ 314,892
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure
Fair value of plan assets at beginning of period	4,150	3,286
Actual return on plan assets	10	(41)
Benefits paid	(385)	(48)
Contributions	461	466
Exchange rate changes	785	487
Fair value of plan assets at end of the period	$ 5,021	$ 4,150

Benefit Plans - Benefit Plan, F

Benefit Plans - Benefit Plan, Future Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Defined Benefit Pension Plans | U.S.
Defined Benefit Plan, Expected Future Benefit Payment
2,019	$ 15,369
2,020	16,253
2,021	16,966
2,022	15,894
2,023	15,823
Years 2024-2028	78,304
Expected future payments	972
Defined Benefit Pension Plans | Foreign
Defined Benefit Plan, Expected Future Benefit Payment
2,019	3,115
2,020	2,769
2,021	2,952
2,022	3,366
2,023	3,630
Years 2024-2028	23,111
Expected future payments	4,334
Supplemental Retirement Plans
Defined Benefit Plan, Expected Future Benefit Payment
2,019	1,105
2,020	1,076
2,021	1,045
2,022	1,009
2,023	970
Years 2024-2028	4,276
Expected future payments	1,105
Other Postretirement Benefits Plans
Defined Benefit Plan, Expected Future Benefit Payment
2,019	581
2,020	514
2,021	388
2,022	313
2,023	272
Years 2024-2028	915
Expected future payments	$ 581

Benefit Plans - 1% Change in Ac

Benefit Plans - 1% Change in Accumulated Postretirement Benefit Obligation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rate
Accumulated postretirement benefit obligation (1 percent increase)	$ 157
Accumulated postretirement benefit obligation (1 percent decrease)	(138)
Periodic postretirement benefit cost (1 percent increase)	6
Periodic postretirement benefit cost (1 percent decrease)	$ (5)

Benefit Plans - Defined Contrib

Benefit Plans - Defined Contribution Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Defined Contribution expense	$ 12,585	$ 13,103	$ 6,864

Earnings per Share - Reconcilia

Earnings per Share - Reconciliation from Basic to Diluted Weighted Average Shares Outstanding (Details) - shares	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Weighted average shares outstanding – Basic (shares)	133,765,294	133,336,352	133,222,463	133,154,144	133,138,140	104,096,837	104,015,815	103,947,888	133,380,567	111,299,670	78,016,005
Dilutive effect of unvested common shares with service conditions and assumed stock option exercises and conversions (shares)									1,304,364	369,367	0
Weighted average shares outstanding – Diluted (shares)	134,987,604	134,576,162	134,209,740	133,884,983	133,895,646	104,096,837	104,015,815	103,947,888	134,684,931	111,669,037	78,016,005

Earnings per Share - Reconcil_2

Earnings per Share - Reconciliation of Net Income (Loss) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income (loss) attributable to PQ Group Holdings Inc.	$ 28,119	$ 14,185	$ 15,782	$ 214	$ 65,011	$ (3,345)	$ (1,609)	$ (2,454)	$ 58,300	$ 57,603	$ (79,746)
Denominator:
Weighted average shares outstanding – Basic (shares)	133,765,294	133,336,352	133,222,463	133,154,144	133,138,140	104,096,837	104,015,815	103,947,888	133,380,567	111,299,670	78,016,005
Weighted average shares outstanding – Diluted (shares)	134,987,604	134,576,162	134,209,740	133,884,983	133,895,646	104,096,837	104,015,815	103,947,888	134,684,931	111,669,037	78,016,005
Net income (loss) per share:
Basic income (loss) per share (usd per share)	$ 0.21	$ 0.11	$ 0.12	$ 0	$ 0.49	$ (0.03)	$ (0.02)	$ (0.02)	$ 0.44	$ 0.52	$ (1.02)
Diluted income (loss) per share (usd per share)	$ 0.21	$ 0.11	$ 0.12	$ 0	$ 0.49	$ (0.03)	$ (0.02)	$ (0.02)	$ 0.43	$ 0.52	$ (1.02)

Earnings per Share - Anti-dilut

Earnings per Share - Anti-dilutive Shares (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Performance based restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares	1,643,760	1,769,447	1,731,522
Performance based stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares	586,253	586,523	417,086
Restricted stock awards and restricted units
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares	10,296	0	751,410
Stock option
Antidilutive Securities Excluded from Computation of Earnings Per Share
Antidilutive shares	863,063	621,747	1,381,352

Stock-Based Compensation - Narr

Stock-Based Compensation - Narratives (Details) - USD ($)	Dec. 27, 2018	Oct. 02, 2017	May 04, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018	Sep. 30, 2017	Oct. 03, 2017
Share-based Compensation Arrangement by Share-based Payment Award
Stock compensation					$ 19,464,000	$ 8,799,000	$ 7,029,000
Tax benefit from exercise of stock options					4,809,000	$ 3,345,000	$ 2,662,000
PQ Holdings, Eco Services
Share-based Compensation Arrangement by Share-based Payment Award
Stock awards transferred as consideration			$ 1,400,000
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award
Stock based compensation expense not yet recognized (options)					$ 2,484,141,000				$ 2,484,141,000
Period for which unrecognized compensation will be recognized					0 years
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award
Nonvested units (shares)				2,482,932	1,770,660	2,096,637	2,482,932		1,770,660
Granted (shares)	14,498	21,067		266,955	14,498	51,907
Period for which unrecognized compensation will be recognized					0 years
Stock based compensation expense not yet recognized (other than options)					$ 342,724,000				$ 342,724,000
Restricted Stock | PQ Holdings, Eco Services
Share-based Compensation Arrangement by Share-based Payment Award
Nonvested units (shares)			2,444,070
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award
Nonvested units (shares)			0	0	998,786	1,654,690	0		998,786
Granted (shares)				0	161,598	1,654,690
Period for which unrecognized compensation will be recognized					0 years
Stock based compensation expense not yet recognized (other than options)					$ 13,945,550,000				$ 13,945,550,000
Performance Awards
Share-based Compensation Arrangement by Share-based Payment Award
Stock compensation					$ 0
Performance Awards | Exit Event Exceeding Threshold
Share-based Compensation Arrangement by Share-based Payment Award
Awards vesting rights percentage					100.00%
Incentive Unit Agreement | Stock Option | Class B units
Share-based Compensation Arrangement by Share-based Payment Award
Granted (weighted average exercise price, usd per share)			$ 1,000					$ 1,000
Options outstanding (shares)			25,093					25,093
Incentive Unit Agreement | Stock Option | Class B units | Annual Vesting as of Dec 1, 2015
Share-based Compensation Arrangement by Share-based Payment Award
Awards vesting rights percentage			25.00%					25.00%
Incentive Unit Agreement | Stock Option | Class B units | Employee
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (shares)			10,674					10,674
Incentive Unit Agreement | Stock Option | Class B units | Employee | Time based
Share-based Compensation Arrangement by Share-based Payment Award
Awards vesting rights percentage			50.00%					50.00%
Incentive Unit Agreement | Stock Option | Class B units | Employee | Performance based
Share-based Compensation Arrangement by Share-based Payment Award
Awards vesting rights percentage			50.00%					50.00%
Incentive Unit Agreement | Stock Option | Class B units | Directors and affiliates
Share-based Compensation Arrangement by Share-based Payment Award
Options outstanding (shares)			14,419					14,419
2016 Stock Incentive Plan | Stock Option
Share-based Compensation Arrangement by Share-based Payment Award
Stock options granted (shares)										7,644,518
Options outstanding (shares)			1,378,302
Expected term (in years)							5 years
Expected volatility							45.79%
Risk-free interest rate							1.54%
Expected dividend yield							0.00%
Shares authorized (shares)			8,017,038
Weighted average exercise price (usd per share)			$ 8.04
Expiration period			10 years						10 years	10 years
2016 Stock Incentive Plan | Stock Option | PQ Holdings, Eco Services
Share-based Compensation Arrangement by Share-based Payment Award
Accelerated compensation cost			$ 1,174,000
2017 Omnibus Incentive Plan | Stock Option
Share-based Compensation Arrangement by Share-based Payment Award
Stock options granted (shares)				538,908	241,316	1,051,496
Granted (weighted average exercise price, usd per share)				$ 8.05	$ 17.50	$ 13.70
Options outstanding (shares)			1,738,527	1,798,438	2,941,154	2,715,170	1,798,438		2,941,154
Expected term (in years)					5 years 9 months
Expected volatility					26.38%
Risk-free interest rate					2.86%
Expected dividend yield					0.00%
Shares reserved for issuance (shares)											7,344,000
Number of shares available for grant (shares)					5,396,119				5,396,119		372,520
Weighted average exercise price (usd per share)			$ 7.80	$ 7.96	$ 10.79	$ 10.18	$ 7.96		$ 10.79

Stock-Based Compensation - 2017

Stock-Based Compensation - 2017 Plan (Details) - 2017 Omnibus Incentive Plan - Stock Option - USD ($) $ / shares in Units, $ in Thousands	8 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding
Beginning balance (shares)	1,738,527	2,715,170	1,798,438
Granted (shares)	538,908	241,316	1,051,496
Exercised (shares)		(15,332)	(32,366)
Forfeited and expired (shares)	(478,997)		(102,398)
Ending balance (shares)	1,798,438	2,941,154	2,715,170
Exercisable (shares)		1,629,969
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price
Beginning balance (weighted average exercise price, usd per share)	$ 7.80	$ 10.18	$ 7.96
Granted (weighted average exercise price, usd per share)	8.05	17.50	13.70
Exercised (weighted average exercise price, usd per share)		8.51	8.04
Forfeited and expired (weighted average exercise price, usd per share)	7.49		7.98
Ending balance (weighted average exercise price, usd per share)	$ 7.96	10.79	$ 10.18
Exercisable (weighted average exercise price, usd per share)		$ 10.19
Outstanding (weighted average contractual term)		7 years 8 months 16 days
Outstanding (aggregate intrinsic value)		$ 14,452
Exercisable (weighted average contractual term)		7 years 8 months 16 days
Exercisable (aggregate intrinsic value)		$ 8,748

Stock-Based Compensation - Assu

Stock-Based Compensation - Assumptions and Methodology (Details) - Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
2016 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology
Expected term (in years)			5 years
Expected volatility			45.79%
Risk-free interest rate			1.54%
Expected dividend yield			0.00%
Weighted average grant date fair value of options granted (usd per share)			$ 3.33
2017 Omnibus Incentive Plan and 2016 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology
Expected term (in years)		5 years 10 months 6 days
Expected volatility		34.85%
Risk-free interest rate		2.00%
Expected dividend yield		0.00%
Weighted average grant date fair value of options granted (usd per share)		$ 4.71
2017 Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology
Expected term (in years)	5 years 9 months
Expected volatility	26.38%
Risk-free interest rate	2.86%
Expected dividend yield	0.00%
Weighted average grant date fair value of options granted (usd per share)	$ 5.47

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock (Details) - $ / shares	Dec. 27, 2018	Oct. 02, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares
Beginning balance nonvested (shares)				2,096,637	2,482,932
Granted (shares)	14,498	21,067	266,955	14,498	51,907
Vested (shares)			(207,915)	(223,298)	(187,837)
Forfeited (shares)			(20,178)	(117,177)	(250,365)
Ending balance nonvested (shares)			2,482,932	1,770,660	2,096,637
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value
Beginning balance nonvested (weighted average grant date fair value, usd per share)			$ 9.27	$ 8.87	$ 9.34
Granted (weighted average grant date fair value, usd per share)			12.32	13.80	16.11
Vested (weighted average grant date fair value, usd per share)			12.32	12.18	12.84
Forfeited (weighted average grant date fair value, usd per share)			10.52	8.04	12.03
Ending balance nonvested (weighted average grant date fair value, usd per share)			$ 9.34	$ 8.39	$ 8.87
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares
Beginning balance nonvested (shares)			0	1,654,690	0
Granted (shares)			0	161,598	1,654,690
Vested (shares)			0	(797,859)	0
Forfeited (shares)			0	(19,643)	0
Ending balance nonvested (shares)			0	998,786	1,654,690
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value
Beginning balance nonvested (weighted average grant date fair value, usd per share)			$ 0	$ 16.97	$ 0
Granted (weighted average grant date fair value, usd per share)			0	16.12	16.97
Vested (weighted average grant date fair value, usd per share)			0	16.97	0
Forfeited (weighted average grant date fair value, usd per share)			0	16.97	0
Ending balance nonvested (weighted average grant date fair value, usd per share)			$ 0	$ 16.83	$ 16.97

Commitments and Contingent Li_3

Commitments and Contingent Liabilities - Narratives (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies
Document Period End Date	Dec. 31, 2018
Rent expense	$ 25,082	$ 22,704	$ 16,315
Purchase commitments	56,642
Subsurface Remedial and Wetlands/Marsh Management
Loss Contingencies
Accrual for environmental loss contingencies	873	1,245
Subsurface Remediation and Soil Vapor Extraction
Loss Contingencies
Accrual for environmental loss contingencies	984	$ 1,220
ABL Facility | ABL Facility | Line of Credit
Loss Contingencies
Letters of credit outstanding	$ 19,796

Commitments and Contingent Li_4

Commitments and Contingent Liabilities - Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity
2,019	$ 18,457
2,020	14,344
2,021	11,432
2,022	8,354
2,023	6,198
Thereafter	17,477
Future minimum lease payments on operating leases	$ 76,262

Commitments and Contingent Li_5

Commitments and Contingent Liabilities - Schedule of Purchase Obligations (Details) $ in Thousands	Dec. 31, 2018USD ($)
Purchase Obligation, Fiscal Year Maturity
2,019	$ 28,485
2,020	19,820
2,021	2,039
2,022	1,450
2,023	1,305
Thereafter	3,543
Total purchase commitments	$ 56,642

Restructuring and Other Relat_3

Restructuring and Other Related Costs - Components of Restructuring and Other Related Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and other related costs	$ 6,208	$ 8,490	$ 12,630
Other related costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other related costs	5,323	2,949	7,537
Eco Services Restructuring Plan | Employee severance
Restructuring Cost and Reserve [Line Items]
Restructuring and other related costs	0	830	5,093
Performance Materials Plant Closure | Employee severance
Restructuring Cost and Reserve [Line Items]
Restructuring and other related costs	$ 885	$ 4,711	$ 0

Restructuring and Other Relat_4

Restructuring and Other Related Costs - Schedule of Restructuring Reserve (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Reserve
Beginning balance	$ 3,338	$ 1,643	$ 1,293
Restructuring charges	581	5,541	5,093
Other adjustments	304
Cash payments	(2,953)	(3,846)	(4,743)
Ending balance	1,270	3,338	1,643
Eco Services Restructuring Plan
Restructuring Reserve
Beginning balance	215	1,643	1,293
Restructuring charges	0	830	5,093
Other adjustments	0
Cash payments	(215)	(2,258)	(4,743)
Ending balance	0	215	1,643
Performance Materials Plant Closure
Restructuring Reserve
Beginning balance	3,123	0	0
Restructuring charges	581	4,711	0
Other adjustments	304
Cash payments	(2,738)	(1,588)	0
Ending balance	$ 1,270	$ 3,123	$ 0

Long-term Supply Contract (Deta

Long-term Supply Contract (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 01, 2014
Commitments and Contingencies Disclosure [Abstract]
Supply agreement liability	$ 0	$ 22,250		$ 27,300
Gain on contract termination	$ 20,612	$ 0	$ 0

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($)	Dec. 11, 2017	Oct. 03, 2017	May 04, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 29, 2014
Related Party Transaction
Management advisory fees				$ 0	$ 3,777,000	$ 3,584,000
Debt extinguishment costs				0	47,875,000	0
Affiliated Entity
Related Party Transaction
Annual monitoring fee							$ 5,000,000
Corporate Joint Venture
Related Party Transaction
Purchases from related party				645,000	2,475,000	1,191,000
INEOS Capital Partners
Related Party Transaction
Related party sales				5,587,000	8,396,000
Unsecured Debt | Floating Rate Senior Unsecured Notes due 2022
Related Party Transaction
Debt instrument face amount			$ 525,000,000
Debt extinguishment costs	$ 6,043,000	$ 32,284,000
Unsecured Debt | Floating Rate Senior Unsecured Notes due 2022 | Board of Directors
Related Party Transaction
Debt instrument face amount			$ 4,000,000
Debt extinguishment costs					338,000
Payment for financing expenses					362,000	300,000
Unsecured Debt | Floating Rate Senior Unsecured Notes due 2022 | LIBOR
Related Party Transaction
Variable rate on spread			10.75%
Debt instrument, interest rate floor			1.00%
Unsecured Debt | Senior Unsecured Notes due 2025
Related Party Transaction
Debt instrument face amount	$ 300,000,000
Operating Lease Rental Payments | Corporate Joint Venture
Related Party Transaction
Related party sales				295,000	295,000	187,000
Manufacturing Costs | Corporate Joint Venture
Related Party Transaction
Related party sales				16,869,000	17,470,000	10,707,000
Services | Corporate Joint Venture
Related Party Transaction
Related party sales				12,727,000	12,248,000	8,169,000
Product Demonstration Costs | Corporate Joint Venture
Related Party Transaction
Related party sales				$ 1,768,000	$ 2,175,000	$ 1,663,000

Quarterly Financial Summary (_3

Quarterly Financial Summary (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 380,041	$ 427,203	$ 434,713	$ 366,197	$ 358,074	$ 391,829	$ 389,267	$ 332,931	$ 1,608,154	$ 1,472,101	$ 1,064,177
Gross profit	87,609	107,500	108,404	78,121	84,151	102,559	107,414	82,712	381,634	376,836	254,092
Operating income	57,459	48,854	49,054	28,189	26,771	46,385	55,080	37,652	183,556	165,888	81,539
Net income (loss)	28,470	14,436	16,159	556	65,564	(3,016)	(1,670)	(2,315)	59,621	58,563	(79,158)
Net income (loss) attributable to PQ Group Holdings Inc.	$ 28,119	$ 14,185	$ 15,782	$ 214	$ 65,011	$ (3,345)	$ (1,609)	$ (2,454)	$ 58,300	$ 57,603	$ (79,746)
Net income (loss) per share:
Basic income (loss) per share (usd per share)	$ 0.21	$ 0.11	$ 0.12	$ 0	$ 0.49	$ (0.03)	$ (0.02)	$ (0.02)	$ 0.44	$ 0.52	$ (1.02)
Diluted income (loss) per share (usd per share)	$ 0.21	$ 0.11	$ 0.12	$ 0	$ 0.49	$ (0.03)	$ (0.02)	$ (0.02)	$ 0.43	$ 0.52	$ (1.02)
Weighted average shares outstanding:
Basic (shares)	133,765,294	133,336,352	133,222,463	133,154,144	133,138,140	104,096,837	104,015,815	103,947,888	133,380,567	111,299,670	78,016,005
Diluted (shares)	134,987,604	134,576,162	134,209,740	133,884,983	133,895,646	104,096,837	104,015,815	103,947,888	134,684,931	111,669,037	78,016,005

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	May 04, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash paid during the year for:
Income taxes, net of refunds		$ 23,842	$ 29,199	$ 16,981
Interest		105,057	170,131	132,579
Non-cash investing activity:
Capital expenditures acquired on account but unpaid as of the year end		23,498	18,762	18,161
PQ Holdings, Eco Services
Non-cash financing activities:
Equity consideration for the Business Combination	$ 910,800	0	0	910,800
Debt assumed		0	0	22,911
Sovitec Mondial S.A.
Non-cash financing activities:
Debt assumed		$ 0	$ 16,609	$ 0

Supplemental Cash Flow Inform_4

Supplemental Cash Flow Information - Cash and Restricted Cash Reconciliation (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash and Restricted Cash Reconciliation [Abstract]
Cash and cash equivalents	$ 57,854	$ 66,195	$ 70,742
Restricted cash included in prepaid and other current assets	1,872	1,048	14,335
Total cash, cash equivalents and restricted cash shown in the consolidated statements of cash flows	$ 59,726	$ 67,243	$ 85,077	$ 25,573

Schedule I - Condensed Statemen

Schedule I - Condensed Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions
Stock compensation									$ 19,464	$ 8,799	$ 5,432
Net income (loss) attributable to PQ Group Holdings Inc.	$ 28,119	$ 14,185	$ 15,782	$ 214	$ 65,011	$ (3,345)	$ (1,609)	$ (2,454)	58,300	57,603	(79,746)
Other comprehensive income (loss), net of tax:
Comprehensive income (loss) attributable to PQ Group Holdings Inc.									14,885	115,625	(134,105)
Parent Company
Condensed Financial Statements, Captions
Stock compensation									19,464	8,799	7,029
Equity in net (income) loss from subsidiaries									(77,764)	(66,402)	72,717
Net income (loss) attributable to PQ Group Holdings Inc.									58,300	57,603	(79,746)
Other comprehensive income (loss), net of tax:
Pension and postretirement benefits									(7,958)	(101)	6,865
Net (loss) gain from hedging activities									(330)	(3,590)	4,557
Foreign currency translation									(35,127)	61,713	(65,781)
Total other comprehensive income (loss)									(43,415)	58,022	(54,359)
Comprehensive income (loss) attributable to PQ Group Holdings Inc.									$ 14,885	$ 115,625	$ (134,105)

Schedule I - Condensed Balance

Schedule I - Condensed Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
ASSETS
Total current assets	$ 558,616	$ 548,968
Total assets	4,327,425	4,415,455
LIABILITIES
Total current liabilities	255,611	288,409
Total liabilities	2,663,280	2,783,536
STOCKHOLDERS' EQUITY
Common stock ($0.01 par); authorized shares 450,000,000; issued shares 135,758,269 and 135,244,379 on December 31, 2018 and 2017, respectively; outstanding shares 135,592,045 and 135,244,379 on December 31, 2018 and 2017, respectively	1,358	1,352
Preferred stock ($0.01 par); authorized shares 50,000,000; no shares issued or outstanding on December 31, 2018 and 2017	0	0
Additional paid-in capital	1,674,703	1,655,114
Retained earnings (accumulated deficit)	25,523	(32,777)
Treasury stock, at cost; shares 166,224 and 0 on December 31, 2018 and 2017, respectively	(2,920)	0
Accumulated other comprehensive (loss) income	(39,104)	4,311
Total PQ Group Holdings Inc. equity	1,659,560	1,628,000
Total liabilities and equity	4,327,425	4,415,455
Parent Company
ASSETS
Total current assets	0	0
Investment in subsidiaries	1,659,560	1,628,000
Total assets	1,659,560	1,628,000
LIABILITIES
Total current liabilities	0	0
Total liabilities	0	0
STOCKHOLDERS' EQUITY
Common stock ($0.01 par); authorized shares 450,000,000; issued shares 135,758,269 and 135,244,379 on December 31, 2018 and 2017, respectively; outstanding shares 135,592,045 and 135,244,379 on December 31, 2018 and 2017, respectively	1,358	1,352
Preferred stock ($0.01 par); authorized shares 50,000,000; no shares issued or outstanding on December 31, 2018 and 2017	0	0
Additional paid-in capital	1,674,703	1,655,114
Retained earnings (accumulated deficit)	25,523	(32,777)
Treasury stock, at cost; shares 166,224 and 0 on December 31, 2018 and 2017, respectively	(2,920)	0
Accumulated other comprehensive (loss) income	(39,104)	4,311
Total PQ Group Holdings Inc. equity	1,659,560	1,628,000
Total liabilities and equity	$ 1,659,560	$ 1,628,000

Schedule I - Condensed Balanc_2

Schedule I - Condensed Balance Sheet Parenthetical (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Stockholders' Equity Attributable to Parent
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized (shares)	450,000,000	450,000,000
Common stock, shares issued (shares)	135,758,269	135,244,379
Common stock, shares outstanding (shares)	135,592,045	135,244,379
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (shares)	50,000,000	50,000,000
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Treasury stock (shares)	166,224	0
Parent Company
Stockholders' Equity Attributable to Parent
Common stock, par value (usd per share)	$ 0.01	$ 0.01
Common stock, shares authorized (shares)	450,000,000	450,000,000
Common stock, shares issued (shares)	135,758,269	135,244,379
Common stock, shares outstanding (shares)	135,592,045	135,244,379
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (shares)	50,000,000	50,000,000
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Treasury stock (shares)	166,224	0

Schedule I - Condensed Statem_2

Schedule I - Condensed Statement of Cash Flow (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income (loss)	$ 28,119	$ 14,185	$ 15,782	$ 214	$ 65,011	$ (3,345)	$ (1,609)	$ (2,454)	$ 58,300	$ 57,603	$ (79,746)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Stock compensation									19,464	8,799	5,432
Net cash provided by operating activities									248,644	165,173	122,708
Cash flows from investing activities:
Net cash used in investing activities									(119,290)	(195,982)	(1,915,763)
Cash flows from financing activities:
IPO proceeds									0	507,500	0
IPO costs									0	(26,804)	0
Net cash (used in) provided by financing activities									(137,225)	19,833	1,858,445
Cash, cash equivalents and restricted cash at beginning of period				66,195				70,742	66,195	70,742
Cash, cash equivalents and restricted cash at end of period	57,854				66,195				57,854	66,195	70,742
Parent Company
Cash flows from operating activities:
Net income (loss)									58,300	57,603	(79,746)
Equity in net (income) loss from subsidiaries									(77,764)	(66,402)	72,717
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Stock compensation									19,464	8,799	7,029
Net cash provided by operating activities									0	0	0
Cash flows from investing activities:
Investment in subsidiaries									0	(480,696)	0
Net cash used in investing activities									0	(480,696)	0
Cash flows from financing activities:
IPO proceeds									0	507,500	0
IPO costs									0	(26,804)	0
Net cash (used in) provided by financing activities									0	480,696	0
Effect of exchange rate changes on cash, cash equivalents and restricted cash									0	0	0
Net change in cash, cash equivalents and restricted cash									0	0	0
Cash, cash equivalents and restricted cash at beginning of period				$ 0				$ 0	0	0	0
Cash, cash equivalents and restricted cash at end of period	$ 0				$ 0				$ 0	$ 0	$ 0