AAON (AAON) 10-K 28 Feb 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 25, 2019	Jun. 30, 2018
Document And Entity Information
Entity Registrant Name	AAON INC
Entity Central Index Key	824,142
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Is Entity a Well-known Seasoned Issuer?	No
Is Entity a Voluntary Filer?	No
Is Entity's Reporting Status Current?	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		51,976,455
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2,018
Entity Public Float			$ 1,360.8
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false

Consolidated Balance Sheets

Consolidated Balance Sheets $ in Millions	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Current assets:
Cash and cash equivalents	$ 1,994,000	$ 21,457,000
Certificates of deposit	0	2,880,000
Debt Securities, Held-to-maturity, Current	0	6,077,000
Accounts receivable, net	54,078,000	50,338,000
Income tax receivable	6,104,000	1,643,000
Note receivable	27,000	28,000
Inventories, net	77,612,000	70,786,000
Prepaid expenses and other	1,046,000	518,000
Total current assets	140,861,000	153,727,000
Property, plant and equipment:
Land	3,114,000	2,233,000
Buildings	97,393,000	92,075,000
Machinery and equipment	212,779,000	184,316,000
Furniture and fixtures	16,597,000	13,714,000
Total property, plant and equipment	329,883,000	292,338,000
Less: Accumulated depreciation	166,880,000	149,963,000
Property, plant and equipment, net	163,003,000	142,375,000
Intangible assets, net	506,000	0
Goodwill	3,229,000	0
Note receivable, long-term	598,000	678,000
Total assets	308,197,000	296,780,000
Current liabilities:
Revolving credit facility	0	0
Accounts payable	10,616,000	10,967,000
Accrued liabilities	37,455,000	39,098,000
Total current liabilities	48,071,000	50,065,000
Deferred revenue	1,655,000	1,512,000
Deferred tax liabilities	10,826,000	7,977,000
Donations	146,000	0
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $.001 par value, 5,000,000 shares authorized, no shares issued	0	0
Common stock, $.004 par value, 100,000,000 shares authorized, 51,991,242 and 52,422,801 issued and outstanding at December 31, 2018 and 2017, respectively	208,000	210,000
Additional paid-in capital	0	0
Retained earnings	247,291,000	237,016,000
Total stockholders’ equity	247,499,000	237,226,000
Total liabilities and stockholders’ equity	$ 308,197,000	$ 296,780,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Stockholders’ equity:
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.004	$ 0.004
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	51,991,242	52,422,801
Common stock, shares outstanding	51,991,242	52,422,801

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net sales	$ 433,947	$ 405,232	$ 383,977
Gross profit	103,533	123,397	118,080
Selling, general and administrative expenses	47,755	49,249	38,506
(Gain) loss on disposal of assets	(12)	45	(20)
Income from operations	55,790	74,103	79,594
Interest income, net	196	298	292
Other (expense) income, net	(47)	91	105
Income before taxes	55,939	74,492	79,991
Income tax provision	13,367	19,994	26,615
Net income	$ 42,572	$ 54,498	$ 53,376
Earnings per share:
Basic (usd per share)	$ 0.81	$ 1.04	$ 1.01
Diluted (usd per share)	0.81	1.03	1
Cash dividends declared per common share	$ 0.32	$ 0.26	$ 0.24
Weighted average shares outstanding:
Basic	52,284,616	52,572,496	52,924,398
Diluted	52,667,939	53,078,734	53,449,754
Product
Net sales	$ 433,947	$ 405,232	$ 383,977
Cost of sales	$ 330,414	$ 281,835	$ 265,897

Consolidated Statements of In_2

Consolidated Statements of Income (Parenthetical)	Jul. 16, 2014
Income Statement [Abstract]
Stock split, conversion ratio	1.5

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings
Balance (in shares) at Dec. 31, 2015		53,012
Balance at Dec. 31, 2015	$ 178,918	$ 212	$ 0	$ 178,706
Net income	53,376			53,376
Stock options exercised and restricted stock awards granted, including tax benefits (in shares)		375
Stock options exercised and restricted stock awards granted, including tax benefits	2,063	$ 2	2,061
Share-based compensation	4,357		4,357
Stock repurchased and retired (in shares)		(736)
Stock repurchased and retired	(20,140)	$ (3)	(6,418)	(13,719)
Dividends	(12,676)			(12,676)
Balance (in shares) at Dec. 31, 2016		52,651
Balance at Dec. 31, 2016	205,898	$ 211	0	205,687
Net income	54,498			54,498
Stock options exercised and restricted stock awards granted, including tax benefits (in shares)		293
Stock options exercised and restricted stock awards granted, including tax benefits	2,259	$ 1	2,258
Share-based compensation	6,458		6,458
Stock repurchased and retired (in shares)		(522)
Stock repurchased and retired	(18,234)	$ (2)	(8,716)	(9,516)
Dividends	(13,653)			(13,653)
Balance (in shares) at Dec. 31, 2017		52,422
Balance at Dec. 31, 2017	237,226	$ 210	0	237,016
Net income	42,572			42,572
Stock options exercised and restricted stock awards granted, including tax benefits (in shares)		353
Stock options exercised and restricted stock awards granted, including tax benefits	4,987	$ 1	4,986
Share-based compensation	7,374		7,374
Stock repurchased and retired (in shares)		(784)
Stock repurchased and retired	(27,943)	$ (3)	(12,360)	(15,580)
Dividends	(16,717)			(16,717)
Balance (in shares) at Dec. 31, 2018		51,991
Balance at Dec. 31, 2018	$ 247,499	$ 208	$ 0	$ 247,291

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Activities
Net income	$ 42,572	$ 54,498	$ 53,376
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	17,655	15,007	13,035
Amortization of bond premiums	13	47	249
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)	174	179	(25)
Provision for excess and obsolete inventories	152	264	625
Share-based compensation	7,374	6,458	4,357
(Gain) loss on disposition of assets	(12)	45	(20)
Foreign currency transaction loss (gain)	55	(59)	(22)
Interest income on note receivable	(27)	(25)	(28)
Deferred income taxes	2,849	(1,554)	825
Changes in assets and liabilities:
Accounts receivable	(2,832)	(7,516)	7,048
Income tax receivable	(4,461)	4,596	(1,537)
Inventories	(5,598)	(23,698)	(9,478)
Prepaid expenses and other	(528)	98	(83)
Accounts payable	(1,176)	3,043	654
Deferred revenue	412	258	417
Accrued liabilities and donations	(1,766)	6,353	(5,470)
Net cash provided by operating activities	54,856	57,994	63,923
Investing Activities
Capital expenditures	(37,268)	(41,713)	(26,604)
Cash paid in business combination	(6,377)	0	0
Proceeds from sale of property, plant and equipment	13	10	28
Investment in certificates of deposits	(7,200)	(5,280)	(4,112)
Maturities of certificates of deposits	10,080	7,912	10,560
Purchase of investments held to maturity	(9,001)	(13,241)	(10,384)
Maturities of investments	14,570	19,700	10,021
Proceeds from called investments	495	1,500	3,514
Principal payments from note receivable	53	60	52
Net cash used in investing activities	(34,635)	(31,052)	(16,925)
Financing Activities
Borrowings under revolving credit facility	0	0	761
Payments under revolving credit facility	0	0	(761)
Stock options exercised	4,987	2,259	2,063
Repurchase of stock	(26,846)	(16,620)	(19,317)
Employee taxes paid by withholding shares	(1,097)	(1,614)	(823)
Cash dividends paid to stockholders	(16,728)	(13,663)	(12,676)
Net cash used in financing activities	(39,684)	(29,638)	(30,753)
Net (decrease) increase in cash and cash equivalents	(19,463)	(2,696)	16,245
Cash and cash equivalents, beginning of year	21,457	24,153	7,908
Cash and cash equivalents, end of year	$ 1,994	$ 21,457	$ 24,153

Business Description

Business Description	12 Months Ended
	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business Description	Business Description AAON, Inc. is a Nevada corporation which was incorporated on August 18, 1987. Our operating subsidiaries include AAON, Inc., an Oklahoma corporation and AAON Coil Products, Inc., a Texas corporation (collectively, the “Company”). The Consolidated Financial Statements include our accounts and the accounts of our subsidiaries. We are engaged in the engineering, manufacturing, marketing and sale of air conditioning and heating equipment consisting of standard, semi-custom and custom rooftop units, chillers, packaged outdoor mechanical rooms, air handling units, makeup air units, energy recovery units, condensing units, geothermal/water-source heat pumps and coils.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Principles of Consolidation These financial statements are prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All inter-company accounts and transactions have been eliminated. Cash and Cash Equivalents We consider all highly liquid temporary investments with original maturity dates of three months or less to be cash equivalents. Cash and cash equivalents consist of bank deposits and highly liquid, interest-bearing money market funds. The Company’s cash and cash equivalents are held in a few financial institutions in amounts that exceed the insurance limits of the Federal Deposit Insurance Corporation. However, management believes that the Company’s counterparty risks are minimal based on the reputation and history of the institutions selected. Investments Certificates of Deposit We held no certificates of deposit at December 31, 2018 and $2.9 million in certificates of deposit at December 31, 2017 . Investments Held to Maturity At December 31, 2018 , we held no investments. We record the amortized cost basis and accrued interest of the corporate notes and bonds in the Consolidated Balance Sheets. We record the interest and amortization of bond premium to interest income in the Consolidated Statements of Income. The following summarizes the amortized cost and estimated fair value of our investments held to maturity at December 31, 2017 : Amortized Cost Gross Unrealized Gain Gross Unrealized (Loss) Fair Value December 31, 2017: Current assets: Investments held to maturity $ 6,077 $ — $ (6 ) $ 6,071 Non current assets: Investments held to maturity — — — — Total $ 6,077 $ — $ (6 ) $ 6,071 We evaluate these investments for other-than-temporary impairments on a quarterly basis. We do not believe there was an other-than-temporary impairment for our investments at December 31, 2017 . Accounts and Note Receivable Accounts and note receivable are stated at amounts due from customers, net of an allowance for doubtful accounts. We generally do not require that our customers provide collateral. The Company determines its allowance for doubtful accounts by considering a number of factors, including the credit risk of specific customers, the customer’s ability to pay current obligations, historical trends, economic and market conditions and the age of the receivable. Accounts are considered past due when the balance has been outstanding for ninety days past negotiated credit terms. Past due accounts are generally written-off against the allowance for doubtful accounts only after all collection attempts have been exhausted. Concentration of Credit Risk Our customers are concentrated primarily in the domestic commercial and industrial new construction and replacement markets. To date, our sales have been primarily to the domestic market, with foreign sales accounting for approximately 3% , 4% , and 4% of revenues for the years ended December 31, 2018 , 2017 , and 2016 , respectively. One customer, Texas AirSystems , accounted for 10% or more of our sales during 2018 , 2017 , or 2016 . No customer accounted for 5% or more of our accounts receivable balance at December 31, 2018 or 2017 . Inventories Inventories are valued at the lower of cost or market using the first-in, first-out (“FIFO”) method. Cost in inventory includes purchased parts and materials, direct labor and applied manufacturing overhead. We establish an allowance for excess and obsolete inventories based on product line changes, the feasibility of substituting parts and the need for supply and replacement parts. Property, Plant and Equipment Property, plant and equipment, including significant improvements, are recorded at cost, net of accumulated depreciation. Repairs and maintenance and any gains or losses on disposition are included in operations. Depreciation is computed using the straight-line method over the following estimated useful lives: Buildings 3-40 years Machinery and equipment 3-15 years Furniture and fixtures 3-7 years Business Combinations We record the assets acquired and liabilities assumed in a business combination at their acquisition date fair values. Fair Value Financial Instruments and Measurements The carrying amounts of cash and cash equivalents, receivables, accounts payable and accrued liabilities approximate fair value because of the short-term maturity of the items. The carrying amount of the Company’s revolving line of credit, and other payables, approximate their fair values either due to their short term nature, the variable rates associated with the debt or based on current rates offered to the Company for debt with similar characteristics. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. Fair value is based upon assumptions that market participants would use when pricing an asset or liability. We use the following fair value hierarchy, which prioritizes valuation technique inputs used to measure fair value into three broad levels: • Level 1: Quoted prices in active markets for identical assets and liabilities that we have the ability to access at the measurement date. • Level 2: Inputs (other than quoted prices included within Level 1) that are either directly or indirectly observable for the asset or liability, including (i) quoted prices for similar assets or liabilities in active markets, (ii) quoted prices for identical or similar assets or liabilities in inactive markets, (iii) inputs other than quoted prices that are observable for the asset or liability, and (iv) inputs that are derived from observable market data by correlation or other means. • Level 3: Unobservable inputs for the asset or liability including situations where there is little, if any, market activity for the asset or liability. Items categorized in Level 3 include the estimated business combination fair values of property, plant and equipment, intangible assets and goodwill. The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable inputs (Level 3). In some cases, the inputs used to measure fair value might fall into different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to a fair value measurement requires judgment, considering factors specific to the asset or liability. Intangible Assets Our intangible assets include various trademarks, service marks and technical knowledge acquired in our February 2018 business combination (see Note 4). We amortize our intangible assets on a straight-line basis over the estimated useful lives of the assets. We evaluate the carrying value of our amortizable intangible assets for potential impairment when events and circumstances warrant such a review. Goodwill Goodwill represents the excess of the consideration paid for the acquired businesses over the fair value of the individual assets acquired, net of liabilities assumed. Goodwill at December 31, 2018 is deductible for income tax purposes. Goodwill is not amortized, but instead is evaluated for impairment at least annually. We perform our annual assessment of impairment during the fourth quarter of our fiscal year, and more frequently if circumstances warrant. To perform this assessment, we first consider qualitative factors to determine whether it is more likely than not that the fair value of the reporting unit exceeds its carrying amount. If we conclude that it is more likely than not that the fair value of a reporting unit does not exceed its carrying amount, we calculate the fair value for the reporting unit and compare the amount to its carrying amount, including goodwill. If the fair value of a reporting unit exceeds its carrying amount, goodwill of the reporting unit is not considered impaired. If the carrying amount of a reporting unit exceeds its fair value, goodwill is considered to be impaired and the goodwill balance is reduced by the difference between the fair value and carrying amount of the reporting unit. We performed a qualitative assessment as of December 31, 2018 to determine whether it was more likely than not that the fair value of the reporting unit was greater than the carrying value of the reporting unit. Based on these qualitative assessments, we determined that the fair value of the reporting unit was more likely than not greater than the carrying value of the reporting unit. Estimates and assumptions used to perform the impairment evaluation are inherently uncertain and can significantly affect the outcome of the analysis. The estimates and assumptions we use in the annual goodwill impairment assessment included market participant considerations and future forecasted operating results. Changes in operating results and other assumptions could materially affect these estimates. Impairment of Long-Lived Assets We review long-lived assets for possible impairment when events or changes in circumstances indicate, in management’s judgment, that the carrying amount of an asset may not be recoverable. Recoverability is measured by a comparison of the carrying amount of an asset or asset group to its estimated undiscounted future cash flows expected to be generated by the asset or asset group. If the undiscounted cash flows are less than the carrying amount of the asset or asset group, an impairment loss is recognized for the amount by which the carrying amount of the asset or asset group exceeds its fair value. Research and Development The costs associated with research and development for the purpose of developing and improving new products are expensed as incurred. For the years ended December 31, 2018 , 2017 , and 2016 research and development costs amounted to approximately $13.5 million , $13.0 million , and $12.0 million , respectively. Advertising Advertising costs are expensed as incurred. Advertising expense for the years ended December 31, 2018 , 2017 , and 2016 was approximately $0.8 million , $1.7 million , and $1.4 million , respectively. Shipping and Handling We incur shipping and handling costs in the distribution of products sold that are recorded in cost of sales. Shipping charges that are billed to the customer are recorded in revenues and as an expense in cost of sales. For the years ended December 31, 2018 , 2017 , and 2016 shipping and handling fees amounted to approximately $12.6 million , $11.4 million , and $10.3 million , respectively. Income Taxes Income taxes are accounted for under the asset and liability method. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the book carrying amounts and the tax basis of assets and liabilities. Excess tax benefits and deficiencies are reported as an income tax benefit or expense on the statement of income and are treated as discrete items to the income tax provision in the reporting period in which they occur. We establish accruals for unrecognized tax positions when it is more likely than not that our tax return positions may not be fully sustained. The Company records a valuation allowance for deferred tax assets when, in the opinion of management, it is more likely than not that deferred tax assets will not be realized. Share-Based Compensation The Company recognizes expense for its share-based compensation based on the fair value of the awards that are granted. The Company’s share-based compensation plans provide for the granting of stock options and restricted stock. The fair values of stock options are estimated at the date of grant using the Black-Scholes-Merton option valuation model. The use of the Black-Scholes-Merton option valuation model requires the input of subjective assumptions. Measured compensation cost is recognized ratably over the vesting period of the related share-based compensation award. Forfeitures are accounted for as they occur. The fair value of restricted stock awards is determined based on the market value of the Company’s shares on the grant date and the compensation expense is recognized on a straight-line basis during the service period of the respective grant. Derivative Instruments In the course of normal operations, the Company occasionally enters into contracts such as forward priced physical contracts for the purchase of raw materials that qualify for and are designated as normal purchase or normal sale contracts. Such contracts are exempted from the fair value accounting requirements and are accounted for at the time product is purchased or sold under the related contract. The Company does not engage in speculative transactions, nor does the Company hold or issue financial instruments for trading purposes. Revenue Recognition On January 1, 2018, we adopted the new accounting standard FASB ASC 606, Revenue from Contracts with Customers , and all the related amendments to all contracts using the retrospective method. The impact at adoption was not material to the consolidated financial statements. The new accounting policy provides results substantially consistent with prior revenue recognition policies. The Company recognizes revenue when it satisfies the performance obligation in its contracts. Most of the Company’s products are highly customized, cannot be resold to other customers and the cost of rework to be resold is not economical. The Company has a formal cancellation policy and generally does not accept returns on these units. As a result, many of the Company’s products do not have an alternative use and therefore, for these products we recognize revenue over the time it takes to produce the unit. For all other products that are part sales or standardized units, we satisfy the performance obligation when the title and risk of ownership pass to the customer, generally at time of shipment. Final sales prices are fixed based on purchase orders. Sales allowances and customer incentives are treated as reductions to sales and are provided for based on historical experiences and current estimates. Sales of our products are moderately seasonal with the peak period being July - November of each year. In addition, the Company presents revenues net of sales tax and net of certain payments to our independent manufacturer representatives (“Representatives”). Representatives are national companies that are in the business of providing HVAC units and other related products and services to customers. The end user customer orders a bundled group of products and services from the Representative and expects the Representative to fulfill the order. Only after the specifications are agreed to by the Representative and the customer, and the decision is made to use an AAON HVAC unit, will we receive notice of the order. We establish the amount we must receive for our HVAC unit (“minimum sales price”), but do not control the total order price that is negotiated by the Representative with the end user customer. We are responsible for billings and collections resulting from all sales transactions, including those initiated by our Representatives. The Representatives submit the total order price to us for invoicing and collection. The total order price includes our minimum sales price and an additional amount which may include both the Representatives’ fee and amounts due for additional products and services required by the customer. These additional products and services may include controls purchased from another manufacturer to operate the unit, start-up services, and curbs for supporting the unit (“Third Party Products”). All are associated with the purchase of a HVAC unit but may be provided by the Representative or another third party. The Company is under no obligation related to Third Party Products. The Representatives’ fee and Third Party Products amounts (“Due to Representatives”) are paid only after all amounts associated with the order are collected from the customer. The amount of payments to our representatives was $47.8 million , $51.8 million , and $55.0 million for each of the years ended December 31, 2018 , 2017 , and 2016 , respectively. The Company also sells extended warranties on parts for various lengths of time ranging from six months to 10 years. Revenue for these separately priced warranties is deferred and recognized on a straight-line basis over the separately priced warranty period. Insurance Reserves Under the Company’s insurance programs, coverage is obtained for significant liability limits as well as those risks required to be insured by law or contract. It is the policy of the Company to self-insure a portion of certain expected losses related primarily to workers’ compensation and medical liability. Provisions for losses expected under these programs are recorded based on the Company’s estimates of the aggregate liabilities for the claims incurred. Product Warranties A provision is made for the estimated cost of maintaining product warranties to customers at the time the product is sold based upon historical claims experience by product line. The Company records a liability and an expense for estimated future warranty claims based upon historical experience and management’s estimate of the level of future claims. Changes in the estimated amounts recognized in prior years are recorded as an adjustment to the liability and expense in the current year. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Because these estimates and assumptions require significant judgment, actual results could differ from those estimates and could have a significant impact on our results of operations, financial position and cash flows. We reevaluate our estimates and assumptions as needed, but at a minimum on a quarterly basis. The most significant estimates include, but are not limited to, the allowance for doubtful accounts, inventory reserves, warranty accrual, workers compensation accrual, medical insurance accrual, share-based compensation and income taxes. Actual results could differ materially from those estimates.

Revenue Recognition

Revenue Recognition	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue Recognition	Revenue Recognition Disaggregated net sales by major source: Years Ending December 31, 2018 2017 2016 (in thousands) Rooftop Units $ 333,105 $ 317,414 $ 309,641 Condensing Units 18,282 19,276 13,987 Air Handlers 21,905 22,570 19,792 Outdoor Mechanical Rooms 2,408 3,238 4,515 Water Source Heat Pumps 14,660 9,911 5,835 Part Sales 26,732 20,756 20,374 Other 16,855 12,067 9,833 Net Sales $ 433,947 $ 405,232 $ 383,977 Other sales include freight, extended warranties and miscellaneous revenue. Disaggregated units sold by major source: Years Ending December 31, 2018 2017 2016 Rooftop Units 15,273 16,003 16,764 Condensing Units 2,007 2,252 1,639 Air Handlers 2,500 2,577 2,114 Outdoor Mechanical Rooms 38 64 65 Water Source Heat Pumps 5,334 2,485 316 Total Units 25,152 23,381 20,898

Business Combination

Business Combination	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Business Combination	Business Combination On February 28, 2018, we closed on the purchase of substantially all of the assets of WattMaster Controls, Inc., (“WattMaster”). The assets acquired consisted primarily of intellectual property, receivables, inventory and fixed assets. The Company also hired substantially all of the WattMaster employees. These assets and workforce will allow us to accelerate the development of our own electronic controllers for air distribution systems. We funded the business combination with available cash of $6.0 million . In May 2018, we paid the final working capital settlement of $0.4 million with available cash. We have included the results of WattMaster’s operations in our consolidated financial statements beginning March 1, 2018. The following table presents the allocation of the consideration paid to the assets acquired and liabilities assumed, based on their fair values, in the acquisition of WattMaster described above: Accounts receivable $ 1,082 Inventories 1,380 Property, plant and equipment 340 Intellectual property 700 Goodwill 3,229 Assumed current liabilities (354 ) Consideration paid $ 6,377 Goodwill represents the excess of the consideration paid for the acquired businesses over the fair value of the individual assets acquired, net of liabilities assumed. Goodwill represents a premium paid to acquire the skilled workforce of the business acquired and is deductible for federal income tax purposes.

Accounts Receivable

Accounts Receivable	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Accounts Receivable	Accounts Receivable Accounts receivable and the related allowance for doubtful accounts are as follows: December 31, 2018 2017 (in thousands) Accounts receivable $ 54,342 $ 50,457 Less: Allowance for doubtful accounts (264 ) (119 ) Total, net $ 54,078 $ 50,338 Years Ending December 31, 2018 2017 2016 Allowance for doubtful accounts: (in thousands) Balance, beginning of period $ 119 $ 90 $ 115 Provisions for losses on accounts receivable, net of adjustments 174 179 (25 ) Accounts receivable written off, net of recoveries (29 ) (150 ) — Balance, end of period $ 264 $ 119 $ 90

Inventories

Inventories	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventories	Inventories The components of inventories and the related changes in the allowance for excess and obsolete inventories are as follows: December 31, 2018 2017 (in thousands) Raw materials $ 67,995 $ 57,784 Work in process 4,060 5,957 Finished goods 6,767 8,163 78,822 71,904 Less: Allowance for excess and obsolete inventories (1,210 ) (1,118 ) Total, net $ 77,612 $ 70,786 Years Ending December 31, 2018 2017 2016 Allowance for excess and obsolete inventories: (in thousands) Balance, beginning of period $ 1,118 $ 1,382 $ 757 Provisions for excess and obsolete inventories 152 102 625 Inventories written off (60 ) (366 ) — Balance, end of period $ 1,210 $ 1,118 $ 1,382

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	Intangible Assets Our intangible assets consist of the following: December 31, 2018 2017 (in thousands) Intellectual property $ 700 $ — Less: Accumulated amortization (194 ) — Total, net $ 506 $ — Amortization expense recorded in cost of sales is as follows: Years Ending December 31, 2018 2017 2016 (in thousands) Amortization expense $ 194 $ — $ —

Note Receivable

Note Receivable	12 Months Ended
	Dec. 31, 2018
Note Receivable [Abstract]
Note Receivable	Note Receivable In connection with the closure of our Canadian facility on May 18, 2009, we sold land and a building in September 2010 and assumed a note receivable from the borrower secured by the property. The C $1.1 million , 15 year note has an interest rate of 4.0% and is payable to us monthly, and has a C $0.6 million balloon payment due in October 2025 . Interest payments are recognized in interest income. We evaluate the note for impairment on a quarterly basis. We determine the note receivable to be impaired if we are uncertain of its collectability based on the contractual terms. At December 31, 2018 and 2017 , there was no impairment.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information Years Ending December 31, 2018 2017 2016 Supplemental disclosures: (in thousands) Interest paid $ 6 $ — $ — Income taxes paid, net 14,979 16,951 27,353 Non-cash investing and financing activities: Non-cash capital expenditures 481 832 270

Warranties

Warranties	12 Months Ended
	Dec. 31, 2018
Guarantees [Abstract]
Warranties	Warranties The Company has warranties with various terms from 18 months for parts to 25 years for certain heat exchangers. The Company has an obligation to replace parts if conditions under the warranty are met. A provision is made for estimated warranty costs at the time the related products are sold based upon the warranty period, historical trends, new products and any known identifiable warranty issues. Changes in the warranty accrual are as follows: Years Ending December 31, 2018 2017 2016 Warranty accrual: (in thousands) Balance, beginning of period $ 10,483 $ 7,936 $ 8,469 Payments made (7,869 ) (8,686 ) (4,134 ) Provisions 9,669 11,233 3,601 Change in estimate (862 ) — — Balance, end of period $ 11,421 $ 10,483 $ 7,936 Warranty expense: $ 8,807 $ 11,233 $ 3,601 The change in estimate relates to the Company’s failure rate calculation. In reviewing claims data, the Company noted specific claims that were the result of an isolated incident and not representative of the Company’s historical performance or representative of expected future claims. As such, these claims were accounted for as a specific accrual for warranty liability and excluded from our failure rate that the Company utilizes in estimating future claims.

Accrued Liabilities

Accrued Liabilities	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued Liabilities	Accrued Liabilities At December 31, accrued liabilities were comprised of the following: December 31, 2018 2017 (in thousands) Warranty $ 11,421 $ 10,483 Due to representatives 11,024 13,086 Payroll 4,182 4,456 Profit sharing 1,835 2,034 Workers' compensation 567 593 Medical self-insurance 1,207 725 Customer prepayments 2,367 2,838 Donations 150 588 Employee vacation time 3,173 2,688 Other 1,529 1,607 Total $ 37,455 $ 39,098

Revolving Credit Facility

Revolving Credit Facility	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Revolving Credit Facility	Revolving Credit Facility Our revolving credit facility, as amended, provides for maximum borrowings of $30.0 million which is provided by BOKF, NA dba Bank of Oklahoma (“Bank of Oklahoma”). Under the line of credit, there was one standby letter of credit totaling $1.3 million as of December 31, 2018 . Borrowings available under the revolving credit facility at December 31, 2018 , were $28.7 million . Interest on borrowings is payable monthly at LIBOR plus 2.0% . No fees are associated with the unused portion of the committed amount. As of December 31, 2018 and 2017 , we had no balance outstanding under our revolving credit facility. The revolving credit facility expires on July 26, 2021. At December 31, 2018 and 2017 , the weighted average interest rate was 4.2% and 3.5% , respectively. At December 31, 2018 , we were in compliance with our financial covenants. These covenants require that we meet certain parameters related to our tangible net worth and total liabilities to tangible net worth ratio. At December 31, 2018 our tangible net worth was $247.5 million , which meets the requirement of being at or above $175.0 million . Our total liabilities to tangible net worth ratio was 0.2 to 1.0, which meets the requirement of not being above 2 to 1.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision (benefit) for income taxes consists of the following: Years Ending December 31, 2018 2017 2016 (in thousands) Current $ 10,518 $ 21,548 $ 25,790 Deferred 2,849 (1,554 ) 825 Total $ 13,367 $ 19,994 $ 26,615 The provision for income taxes differs from the amount computed by applying the statutory federal income tax rate before the provision for income taxes. The reconciliation of the federal statutory income tax rate to the effective income tax rate is as follows: Years Ending December 31, 2018 2017 2016 Federal statutory rate 21 % 35 % 35 % State income taxes, net of federal benefit 6 % 5 % 5 % Remeasurement of deferred taxes — % (6 )% — % Domestic manufacturing deduction — % (3 )% (3 )% Excess tax benefits (2 )% (3 )% (3 )% Other (1 )% (1 )% (1 )% 24 % 27 % 33 % The Tax Cuts and Jobs Act (the “Act”) was enacted on December 22, 2017. Major changes under the Act include the following: • Reducing the corporate rate to 21 percent • Doubling bonus depreciation to 100 percent for five years • Further limitations on executive compensation deductions • Eliminating the domestic manufacturing deduction As a result of these changes, the Company adjusted its deferred tax assets and liabilities in 2017 using the newly enacted rates for the periods when they are expected to be realized. The remeasurement in 2017 resulted in a benefit to income taxes of $4.4 million . The new bonus depreciation provisions resulted in the Company taking $3.2 million of bonus depreciation in 2017. The Company also has historically taken the domestic manufacturing deduction. The Company will no longer receive the benefit of this deduction which typically has lowered our effective tax rate by 3.0% . The Company sometimes has executive compensation that exceeds the $1.0 million limitation. Typically the limit is exceeded due to the volume of stock activity performed by the executives during the year. The limit could also be exceeded by the Chief Executive Officer receiving the maximum amount under our executive annual cash incentive bonus plan. Any compensation that exceeded this limitation in 2018 and in the future will be a permanent difference and cause an increase to our income tax provision. Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amount used for income tax purposes. The significant components of the Company’s deferred tax assets and liabilities are as follows: December 31, 2018 2017 (in thousands) Deferred income tax assets (liabilities): Accounts receivable and inventory reserves $ 401 $ 318 Warranty accrual 3,105 2,698 Other accruals 2,445 1,395 Share-based compensation 1,697 1,432 Donations 80 152 Other, net 851 698 Total deferred income tax assets 8,579 6,693 Property & equipment (19,405 ) (14,670 ) Total deferred income tax liabilities $ (19,405 ) $ (14,670 ) Net deferred income tax liabilities $ (10,826 ) $ (7,977 ) We file income tax returns in the U.S., state and foreign income tax returns jurisdictions. We are subject to U.S. examinations for tax years 2014 to present, and to non-U.S. income tax examinations for the tax years 2014 to present. In addition, we are subject to state and local income tax examinations for tax years 2014 to present. The Company continues to evaluate its need to file returns in various state jurisdictions. Any interest or penalties would be recognized as a component of income tax expense.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation	Share-Based Compensation On May 22, 2007, our stockholders adopted a Long-Term Incentive Plan (“LTIP”) which provided an additional 3.3 million shares that could be granted in the form of stock options, stock appreciation rights, restricted stock awards, performance units and performance awards, in addition to the shares from the previous plan, the 1992 Plan. Since inception of the LTIP, non-qualified stock options and restricted stock awards have been granted with a five year vesting schedule. Under the LTIP, the exercise price of shares granted may not be less than 100% of the fair market value at the date of the grant. On May 24, 2016, our stockholders adopted the 2016 Long-Term Incentive Plan (“2016 Plan”) which provides for approximately 6.4 million shares, comprised of 3.4 million new shares provided for under the 2016 Plan, approximately 0.4 million shares that were available for issuance under the previous LTIP that are now authorized for issuance under the 2016 Plan, and an additional 2.6 million shares that were approved by the stockholders on May 15, 2018. Under the 2016 Plan, shares can be granted in the form of stock options, stock appreciation rights, restricted stock awards, performance awards, dividend equivalent rights, and other awards. Under the 2016 Plan, the exercise price of shares granted may not be less than 100% of the fair market value at the date of the grant. The 2016 Plan is administered by the Compensation Committee of the Board of Directors or such other committee of the Board of Directors as is designated by the Board of Directors (the “Committee”). Membership on the Committee is limited to independent directors. The Committee may delegate certain duties to one or more officers of the Company as provided in the 2016 Plan. The Committee determines the persons to whom awards are to be made, determines the type, size and terms of awards, interprets the 2016 Plan, establishes and revises rules and regulations relating to the 2016 Plan and makes any other determinations that it believes necessary for the administration of the 2016 Plan. The total pre-tax compensation cost related to unvested stock options not yet recognized as of December 31, 2018 is $14.3 million and is expected to be recognized over a weighted-average period of 2.29 years. The following weighted average assumptions were used to determine the fair value of the stock options granted on the original grant date for expense recognition purposes for options granted during December 31, 2018 , 2017 , and 2016 using a Black Scholes-Merton Model: 2018 2017 2016 Director and Officers: Expected dividend yield $ 0.26 $ 0.26 $ 0.22 Expected volatility 29.73 % 30.81 % 41.19 % Risk-free interest rate 2.20 % 1.90 % 2.00 % Expected life (in years) 5.00 5.00 7.68 Employees: Expected dividend yield $ 0.26 $ 0.26 $ 0.25 Expected volatility 29.82 % 30.67 % 34.50 % Risk-free interest rate 2.51 % 1.89 % 1.73 % Expected life (in years) 5.00 5.00 5.69 The expected term of the options is based on evaluations of historical and expected future employee exercise behavior. The risk-free interest rate is based on the U.S. Treasury rates at the date of grant with maturity dates approximately equal to the expected life at the grant date. Volatility is based on historical volatility of our stock over time periods equal to the expected life at grant date. The following is a summary of stock options vested and exercisable as of December 31, 2018 : Weighted Average Weighted Range of Number Remaining Average Exercise of Contractual Exercise Intrinsic Prices Shares Life Price Value (in thousands) $5.67 - 32.80 456,223 5.72 $ 20.25 $ 6,757 $32.85 - 34.10 42,552 7.47 33.95 47 $34.15 - 42.94 17,202 8.30 35.19 7 Total 515,977 5.95 $ 21.88 $ 6,811 The following is a summary of stock options vested and exercisable as of December 31, 2017 : Weighted Average Weighted Range of Number Remaining Average Exercise of Contractual Exercise Intrinsic Prices Shares Life Price Value (in thousands) $4.54 - 22.76 424,130 4.36 $ 12.41 $ 10,303 $23.57 - 32.85 107,456 8.31 30.10 709 $32.90 - 37.30 25,725 9.19 34.07 68 Total 557,311 5.35 $ 16.82 $ 11,080 The following is a summary of stock options vested and exercisable as of December 31, 2016 : Weighted Average Weighted Range of Number Remaining Average Exercise of Contractual Exercise Intrinsic Prices Shares Life Price Value (in thousands) $4.54 - 20.92 338,308 4.75 $ 8.03 $ 8,465 $20.96 - 26.50 71,928 8.56 22.50 759 Total 410,236 5.42 $ 10.57 $ 9,224 A summary of option activity under the plans is as follows: Weighted Average Exercise Options Shares Price Outstanding at December 31, 2017 1,567,109 $ 25.27 Granted 1,480,490 34.49 Exercised (282,598 ) 17.64 Forfeited or Expired (319,152 ) 32.84 Outstanding at December 31, 2018 2,445,849 $ 30.77 Exercisable at December 31, 2018 515,977 $ 21.89 The total intrinsic value of options exercised during the year ended December 31, 2018 , 2017 , and 2016 was $5.4 million , $4.5 million , and $4.9 million , respectively. The cash received from options exercised during the year eneded December 31, 2018 , 2017 , and 2016 was $5.0 million , $2.3 million , and $2.1 million , respectively. The impact of these cash receipts is included in financing activities in the accompanying Consolidated Statements of Cash Flows. Since 2007, as part of the LTIP and since May 2016 as part of the 2016 Plan, the Compensation Committee of the Board of Directors has authorized and issued restricted stock awards to directors and certain key employees. Restricted stock awards granted to directors vest one-third each year. All other restricted stock awards vest at a rate of 20% per year. The fair value of restricted stock awards is based on the fair market value of AAON common stock on the respective grant dates, reduced for the present value of dividends. These awards are recorded at their fair value on the date of grant and compensation cost is recorded using straight-line vesting over the service period. At December 31, 2018 , unrecognized compensation cost related to unvested restricted stock awards was approximately $6.1 million which is expected to be recognized over a weighted average period of 1.84 years. A summary of the unvested restricted stock awards is as follows: Weighted Average Grant date Restricted stock Shares Fair Value Unvested at December 31, 2017 341,800 $ 25.52 Granted 112,075 32.20 Vested (124,508 ) 23.61 Forfeited (36,917 ) 28.37 Unvested at December 31, 2018 292,450 $ 28.54 A summary of share-based compensation is as follows for the years ending December 31, 2018 , 2017 , and 2016 : 2018 2017 2016 Grant date fair value of awards during the period: (in thousands) Options $ 12,932 $ 3,699 $ 6,102 Restricted stock 3,609 4,217 3,147 Total $ 16,541 $ 7,916 $ 9,249 2018 2017 2016 Share-based compensation expense: (in thousands) Options $ 4,181 $ 2,904 $ 1,681 Restricted stock 3,193 3,554 2,676 Total $ 7,374 $ 6,458 $ 4,357 2018 2017 2016 Income tax benefit related to share-based compensation: (in thousands) Options $ 980 $ 1,413 $ 1,610 Restricted stock 353 1,051 458 Total $ 1,333 $ 2,464 $ 2,068

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Employee Benefits	Employee Benefits Defined Contribution Plan - 401(k ) - We sponsor a defined contribution plan (the “Plan”). Eligible employees may make contributions in accordance with the Plan and IRS guidelines. In addition to the traditional 401(k), eligible employees are given the option of making an after-tax contribution to a Roth 401(k) or a combination of both. The Plan provides for automatic enrollment and for an automatic increase to the deferral percentage at January 1st of each year and each year thereafter. Eligible employees are automatically enrolled in the Plan at a 6% deferral rate and currently contributing employees deferral rates will be increased to 6% unless their current rate is above 6% or the employee elects to decline the automatic enrollment or increase. The Plan was amended such that the Company matches 175% up to 6% of employee contributions of eligible compensation. Administrative expenses are paid for by Plan participants. Additionally, Plan participant forfeitures are used to reduce the cost of the Company contributions. For the years ended December 31, 2018 , 2017 , and 2016 we made contributions of $8.1 million , $6.1 million , and $5.9 million , respectively. The Company paid no administrative expenses for the years ended 2018 and 2017 and approximately $0.04 million for the year ended 2016 . Profit Sharing Bonus Plan - We maintain a discretionary profit sharing bonus plan under which approximately 10% of pre-tax profit is paid to eligible employees on a quarterly basis in order to reward employee productivity. Eligible employees are regular full-time employees who are actively employed and working on the first and last days of the calendar quarter and who were employed full-time for at least three full months prior to the beginning of the calendar quarter. Profit sharing expense was $6.2 million , $8.4 million , and $9.0 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively.

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Shareholders' Equity	Stockholders’ Equity Stock Repurchase - The Board has authorized three stock repurchase programs for the Company. The Company may purchase shares on the open market from time to time, up to a total of 5.7 million shares. The Board must authorize the timing and amount of these purchases. Effective May 24, 2016, the Board authorized up to $25.0 million in open market repurchases and on June 2, 2016, the Company executed a repurchase agreement in accordance with the rules and regulations of the SEC allowing the Company to repurchase an aggregate amount of $25.0 million or a total of approximately 2.0 million shares from the open market. The repurchase agreement expired on April 15, 2017. In May 2018, the Board authorized up to $15.0 million in open market repurchases and on May 18, 2018, the Company executed a repurchase agreement in accordance with the rules and regulations of the SEC allowing the Company to repurchase shares from the open market. The agreement expires on March 1, 2019. The Company also has a stock repurchase arrangement by which employee-participants in our 401(k) savings and investment plan are entitled to have shares in AAON, Inc. stock in their accounts sold to the Company. The maximum number of shares to be repurchased is contingent upon the number of shares sold by employee-participants. Lastly, the Company repurchases shares of AAON, Inc. stock from certain of its directors and employees for payment of statutory tax withholdings on stock transactions. All other repurchases from directors or employees are contingent upon Board approval. All repurchases are done at current market prices. Our repurchase activity is as follows: 2018 2017 2016 Program Shares Total $ $ per share Shares Total $ $ per share Shares Total $ $ per share Open market 252,272 $ 8,373,698 $ 33.19 8,676 $ 283,654 $ 32.69 165,598 $ 4,440,658 $ 26.82 401(k) 497,753 18,472,442 37.11 467,580 16,336,084 34.94 540,501 14,875,850 27.52 Directors & employees 33,751 1,096,625 32.49 45,878 1,614,425 35.19 30,072 823,446 27.38 Total 783,776 $ 27,942,765 $ 35.65 522,134 $ 18,234,163 $ 34.92 736,171 $ 20,139,954 $ 27.36 Inception to Date Program Shares Total $ $ per share Open market 4,095,767 $ 69,605,813 $ 16.99 401(k) 7,047,776 100,541,247 14.27 Directors & employees 1,953,261 18,374,658 9.41 Total 13,096,804 $ 188,521,718 $ 14.39 Dividends - At the discretion of the Board of Directors, we pay semi-annual cash dividends. Board approval is required to determine the date of declaration and amount for each semi-annual dividend payment. Our recent dividends are as follows: Declaration Date Record Date Payment Date Dividend per Share May 24, 2016 June 10, 2016 July 1, 2016 $0.11 November 9, 2016 December 2, 2016 December 23, 2016 $0.13 May 16, 2017 June 9, 2017 July 7, 2017 $0.13 November 7, 2017 November 30, 2017 December 21, 2017 $0.13 May 18, 2018 June 8, 2018 July 6, 2018 $0.16 November 8, 2018 November 29, 2018 December 20, 2018 $0.16 We paid cash dividends of $16.7 million , $13.7 million , and $12.7 million in 2018 , 2017 , and 2016 , respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies We are subject to various claims and legal actions that arise in the ordinary course of business. We closely monitor these claims and legal actions and frequently consult with our legal counsel to determine whether they may, when resolved, have a material adverse effect on our financial position, results of operations or cash flows and we accrue and/or disclose loss contingencies as appropriate. We have concluded that the likelihood is remote that the ultimate resolution of any pending litigation or claims will be material or have a material adverse effect on the Company’s business, financial position, results of operations or cash flows. We are occasionally party to short-term, cancellable and occasionally non-cancellable, fixed price contracts with major suppliers for the purchase of raw material and component parts. We expect to receive delivery of raw materials for use in our manufacturing operations. These contracts are not accounted for as derivative instruments because they meet the normal purchase and normal sales exemption. At December 31, 2018 , we had one material contractual purchase obligation for approximately $2.2 million that expires in December 2019.

New Accounting Pronouncements

New Accounting Pronouncements	12 Months Ended
	Dec. 31, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Pronouncements	New Accounting Pronouncements Changes to U.S. GAAP are established by the Financial Accounting Standards Board (“FASB”) in the form of accounting standards updates (“ASUs”) to the FASB’s Accounting Standards Codification. We consider the applicability and impact of all ASUs. ASUs not listed below were assessed and determined to be either not applicable or are expected to have minimal impact on our consolidated financial statements and notes thereto. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . The ASU will replace previous lease accounting guidance in U.S. GAAP. The ASU requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases. The ASU retains a distinction between finance leases and operating leases. The ASU is effective for the Company beginning January 1, 2019. The following ASUs have been issued in 2018 with the same effective dates and transition requirements: • ASU 2018-01, Land Easement Practical Expedient , which provides a relief from certain land easements held before the effective date. • ASU 2018-10, Leases: Codification Improvements , which provides clarification for various areas of Topic 842. • ASU 2018-11, Leases: Targeted Improvements , which provides clarification for several areas of Topic 842: comparative reporting requirements, an optional method of adoption (the transition method) and separating lease and non lease component for lessors. • ASU 2018-20, Leases: Narrow-Scope Improvement for Lessors , which provided clarification to lessors for sales taxes, variable payments and other costs. The Company historically does not enter into numerous or material lease agreements to support its manufacturing operations. The Company typically enters into lease agreements that are less than a year and for leases on assets such as warehouse vehicles and office equipment. The Company assumed a multi-year facility lease in the WattMaster acquisition. The Company has completed the process of determining our contracts to which this new guidance applies. The Company does not expect this new guidance to have a significant impact on the consolidated financial statements due to the non-material monetary amount of the total leased assets under the new applicable guidance. Furthermore, we have elected to apply the short-term lease accounting policy election to all short-term leases under the applicable guidance. Under the policy election the lessee does not recognize a short-term lease liability or right-of-use asset on its balance sheet. The Company will elect the transition method, which becomes effective upon the date of adoption of ASU 2016-02 discussed above. The transition method allows entities to initially apply the new leases standard at the adoption date (January 1, 2019) and recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We expect the cumulative-effect adjustments to the opening balance to be immaterial to the financial statements as a whole. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurements: Changes to the Disclosure Requirement for Fair Value Measurements . The ASU includes additional disclosure requirements for unrealized gains and losses for Level 3 fair value measurement and significant observable inputs used to develop Level 3 fair value measurements. The ASU is effective for the Company beginning after December 15, 2019. We do not expect ASU 2018-13 will have a material effect on our consolidated financial statements and notes thereto. In January 2017, the FASB issued ASU 2017-04, Intangibles-Goodwill and Other . The ASU simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. We will be required to perform our annual goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. In the event the carrying amount exceeds the reporting unit’s fair value, a goodwill impairment charge for the excess will be recorded (not exceeding the recorded amount of the reporting unit’s goodwill). The ASU is effective for the Company beginning April 1, 2020, and requires a prospective method of adoption, although early adoption is permitted for annual goodwill impairment tests performed on testing dates on or after January 1, 2017. We adopted this ASU effective January 1, 2018.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share Basic net income per share is calculated by dividing net income by the weighted average number of shares of common stock outstanding during the period. Diluted net income per share assumes the conversion of all potentially dilutive securities and is calculated by dividing net income by the sum of the weighted average number of shares of common stock outstanding plus all potentially dilutive securities. Dilutive common shares consist primarily of stock options and restricted stock awards. The following table sets forth the computation of basic and diluted earnings per share: 2018 2017 2016 Numerator: (in thousands, except share and per share data) Net income $ 42,572 $ 54,498 $ 53,376 Denominator: Basic weighted average shares 52,284,616 52,572,496 52,924,398 Effect of dilutive stock options and restricted stock 383,323 506,238 525,356 Diluted weighted average shares 52,667,939 53,078,734 53,449,754 Earnings per share: Basic $ 0.81 $ 1.04 $ 1.01 Dilutive $ 0.81 $ 1.03 $ 1.00 Anti-dilutive shares: Shares 1,920,313 785,825 469,603

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Parties	Related Parties The Company purchases some supplies from an entity controlled by the Company’s CEO. The Company sometimes makes sales to the CEO for parts. Additionally, the Company sells units to an entity owned by a member of the President's immediate family. This entity is also one of the Company’s Representatives and as such, the Company makes payments to the entity for third party products. All related party transactions are made on standard Company terms. Following is a summary of transactions and balances with affiliates: Years Ending December 31, 2018 2017 2016 (in thousands) Sales to affiliates $ 1,442 $ 1,579 $ 1,671 Payments to affiliates 342 432 697 December 31, 2018 2017 (in thousands) Due from affiliates $ 79 $ 9 Due to affiliates — —

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On January 31, 2019, the Board of Directors authorized the Company to grant up to (i) 77,434 shares of restricted stock and (ii) 840,000 stock options to non-officer employees, with such awards to be made on March 11, 2019, subject to eligibility requirements and other restrictions as set forth in the Company’s 2016 Plan. Subsequent to December 31, 2018 and through February 25, 2019, the Company repurchased 5,799 shares for $0.2 million from the open market and 58,386 shares for $2.2 million from our 401(k) savings and investment plan.

Quarterly Results (Unaudited)

Quarterly Results (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results (Unaudited)	Quarterly Results (Unaudited) The following is a summary of the quarterly results of operations for the years ending December 31, 2018 and 2017 : Quarter First Second Third Fourth (in thousands, except per share data) 2018 Net sales $ 99,082 $ 109,588 $ 112,937 $ 112,340 Gross profit 15,390 27,585 32,763 27,795 Net income 4,260 11,691 14,085 12,536 Earnings per share: Basic $ 0.08 $ 0.22 $ 0.27 $ 0.24 Diluted $ 0.08 $ 0.22 $ 0.27 $ 0.24 2017 Net sales $ 86,078 $ 101,326 $ 113,668 $ 104,160 Gross profit 24,986 31,678 35,658 31,075 Net income 10,217 13,794 14,717 15,770 Earnings per share: Basic $ 0.19 $ 0.26 $ 0.28 $ 0.30 Diluted $ 0.19 $ 0.26 $ 0.28 $ 0.30

Segments

Segments	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Segments	Segments The following table summarizes certain financial data related to our segments. Transactions between segments are recorded based on prices negotiated between the segments. Sales of units represents the selling price of our units plus freight and other miscellaneous charges less any returns and allowances. Parts includes sales of purchased and fabricated parts including our coils along with the related freight and less any returns and allowances. The “Other” category in the table below includes certain sales cost and expenses that are not allocated to the reportable segments. Asset information by segment is not easily identifiable or reviewed by the chief operating decision maker. As such, this information is not included below. Years Ending December 31, 2018 2017 2016 (in thousands) Sales Units 406,331 384,853 363,666 Parts - External 28,456 22,050 21,692 Parts - Inter-segment 29,385 29,293 25,406 Other (840 ) (1,671 ) (1,381 ) Eliminations (29,385 ) (29,293 ) (25,406 ) Net sales 433,947 405,232 383,977 Gross Profit Units 108,214 128,571 120,940 Parts - External 13,215 9,377 9,967 Parts - Inter-segment 865 426 (105 ) Other (17,896 ) (14,551 ) (12,827 ) Eliminations (865 ) (426 ) 105 Net gross profit 103,533 123,397 118,080

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation These financial statements are prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All inter-company accounts and transactions have been eliminated.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid temporary investments with original maturity dates of three months or less to be cash equivalents. Cash and cash equivalents consist of bank deposits and highly liquid, interest-bearing money market funds. The Company’s cash and cash equivalents are held in a few financial institutions in amounts that exceed the insurance limits of the Federal Deposit Insurance Corporation. However, management believes that the Company’s counterparty risks are minimal based on the reputation and history of the institutions selected.
Investments	Investments Certificates of Deposit We held no certificates of deposit at December 31, 2018 and $2.9 million in certificates of deposit at December 31, 2017 . Investments Held to Maturity At December 31, 2018 , we held no investments. We record the amortized cost basis and accrued interest of the corporate notes and bonds in the Consolidated Balance Sheets. We record the interest and amortization of bond premium to interest income in the Consolidated Statements of Income. The following summarizes the amortized cost and estimated fair value of our investments held to maturity at December 31, 2017 : Amortized Cost Gross Unrealized Gain Gross Unrealized (Loss) Fair Value December 31, 2017: Current assets: Investments held to maturity $ 6,077 $ — $ (6 ) $ 6,071 Non current assets: Investments held to maturity — — — — Total $ 6,077 $ — $ (6 ) $ 6,071 We evaluate these investments for other-than-temporary impairments on a quarterly basis. We do not believe there was an other-than-temporary impairment for our investments at December 31, 2017 .
Accounts and Note Receivable	Accounts and Note Receivable Accounts and note receivable are stated at amounts due from customers, net of an allowance for doubtful accounts. We generally do not require that our customers provide collateral. The Company determines its allowance for doubtful accounts by considering a number of factors, including the credit risk of specific customers, the customer’s ability to pay current obligations, historical trends, economic and market conditions and the age of the receivable. Accounts are considered past due when the balance has been outstanding for ninety days past negotiated credit terms. Past due accounts are generally written-off against the allowance for doubtful accounts only after all collection attempts have been exhausted.
Concentration of Credit Risk	Concentration of Credit Risk Our customers are concentrated primarily in the domestic commercial and industrial new construction and replacement markets. To date, our sales have been primarily to the domestic market, with foreign sales accounting for approximately 3% , 4% , and 4% of revenues for the years ended December 31, 2018 , 2017 , and 2016 , respectively. One customer, Texas AirSystems , accounted for 10% or more of our sales during 2018 , 2017 , or 2016 . No customer accounted for 5% or more of our accounts receivable balance at December 31, 2018 or 2017 .
Inventories	Inventories Inventories are valued at the lower of cost or market using the first-in, first-out (“FIFO”) method. Cost in inventory includes purchased parts and materials, direct labor and applied manufacturing overhead. We establish an allowance for excess and obsolete inventories based on product line changes, the feasibility of substituting parts and the need for supply and replacement parts.
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment, including significant improvements, are recorded at cost, net of accumulated depreciation. Repairs and maintenance and any gains or losses on disposition are included in operations. Depreciation is computed using the straight-line method over the following estimated useful lives: Buildings 3-40 years Machinery and equipment 3-15 years Furniture and fixtures 3-7 years
Business Combinations	Business Combinations We record the assets acquired and liabilities assumed in a business combination at their acquisition date fair values.
Fair Value of Financial Instruments	The carrying amounts of cash and cash equivalents, receivables, accounts payable and accrued liabilities approximate fair value because of the short-term maturity of the items. The carrying amount of the Company’s revolving line of credit, and other payables, approximate their fair values either due to their short term nature, the variable rates associated with the debt or based on current rates offered to the Company for debt with similar characteristics.
Fair Value Measurements	Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the measurement date. Fair value is based upon assumptions that market participants would use when pricing an asset or liability. We use the following fair value hierarchy, which prioritizes valuation technique inputs used to measure fair value into three broad levels: • Level 1: Quoted prices in active markets for identical assets and liabilities that we have the ability to access at the measurement date. • Level 2: Inputs (other than quoted prices included within Level 1) that are either directly or indirectly observable for the asset or liability, including (i) quoted prices for similar assets or liabilities in active markets, (ii) quoted prices for identical or similar assets or liabilities in inactive markets, (iii) inputs other than quoted prices that are observable for the asset or liability, and (iv) inputs that are derived from observable market data by correlation or other means. • Level 3: Unobservable inputs for the asset or liability including situations where there is little, if any, market activity for the asset or liability. Items categorized in Level 3 include the estimated business combination fair values of property, plant and equipment, intangible assets and goodwill. The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable inputs (Level 3). In some cases, the inputs used to measure fair value might fall into different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to a fair value measurement requires judgment, considering factors specific to the asset or liability.
Intangible Assets	Intangible Assets Our intangible assets include various trademarks, service marks and technical knowledge acquired in our February 2018 business combination (see Note 4). We amortize our intangible assets on a straight-line basis over the estimated useful lives of the assets. We evaluate the carrying value of our amortizable intangible assets for potential impairment when events and circumstances warrant such a review.
Goodwill	Goodwill Goodwill represents the excess of the consideration paid for the acquired businesses over the fair value of the individual assets acquired, net of liabilities assumed. Goodwill at December 31, 2018 is deductible for income tax purposes. Goodwill is not amortized, but instead is evaluated for impairment at least annually. We perform our annual assessment of impairment during the fourth quarter of our fiscal year, and more frequently if circumstances warrant. To perform this assessment, we first consider qualitative factors to determine whether it is more likely than not that the fair value of the reporting unit exceeds its carrying amount. If we conclude that it is more likely than not that the fair value of a reporting unit does not exceed its carrying amount, we calculate the fair value for the reporting unit and compare the amount to its carrying amount, including goodwill. If the fair value of a reporting unit exceeds its carrying amount, goodwill of the reporting unit is not considered impaired. If the carrying amount of a reporting unit exceeds its fair value, goodwill is considered to be impaired and the goodwill balance is reduced by the difference between the fair value and carrying amount of the reporting unit. We performed a qualitative assessment as of December 31, 2018 to determine whether it was more likely than not that the fair value of the reporting unit was greater than the carrying value of the reporting unit. Based on these qualitative assessments, we determined that the fair value of the reporting unit was more likely than not greater than the carrying value of the reporting unit. Estimates and assumptions used to perform the impairment evaluation are inherently uncertain and can significantly affect the outcome of the analysis. The estimates and assumptions we use in the annual goodwill impairment assessment included market participant considerations and future forecasted operating results. Changes in operating results and other assumptions could materially affect these estimates.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets We review long-lived assets for possible impairment when events or changes in circumstances indicate, in management’s judgment, that the carrying amount of an asset may not be recoverable. Recoverability is measured by a comparison of the carrying amount of an asset or asset group to its estimated undiscounted future cash flows expected to be generated by the asset or asset group. If the undiscounted cash flows are less than the carrying amount of the asset or asset group, an impairment loss is recognized for the amount by which the carrying amount of the asset or asset group exceeds its fair value.
Research and Development	Research and Development The costs associated with research and development for the purpose of developing and improving new products are expensed as incurred. For the years ended December 31, 2018 , 2017 , and 2016 research and development costs amounted to approximately $13.5 million , $13.0 million , and $12.0 million , respectively.
Advertising	Advertising Advertising costs are expensed as incurred. Advertising expense for the years ended December 31, 2018 , 2017 , and 2016 was approximately $0.8 million , $1.7 million , and $1.4 million , respectively.
Shipping and Handling	Shipping and Handling We incur shipping and handling costs in the distribution of products sold that are recorded in cost of sales. Shipping charges that are billed to the customer are recorded in revenues and as an expense in cost of sales. For the years ended December 31, 2018 , 2017 , and 2016 shipping and handling fees amounted to approximately $12.6 million , $11.4 million , and $10.3 million , respectively.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the book carrying amounts and the tax basis of assets and liabilities. Excess tax benefits and deficiencies are reported as an income tax benefit or expense on the statement of income and are treated as discrete items to the income tax provision in the reporting period in which they occur. We establish accruals for unrecognized tax positions when it is more likely than not that our tax return positions may not be fully sustained. The Company records a valuation allowance for deferred tax assets when, in the opinion of management, it is more likely than not that deferred tax assets will not be realized.
Share-Based Compensation	Share-Based Compensation The Company recognizes expense for its share-based compensation based on the fair value of the awards that are granted. The Company’s share-based compensation plans provide for the granting of stock options and restricted stock. The fair values of stock options are estimated at the date of grant using the Black-Scholes-Merton option valuation model. The use of the Black-Scholes-Merton option valuation model requires the input of subjective assumptions. Measured compensation cost is recognized ratably over the vesting period of the related share-based compensation award. Forfeitures are accounted for as they occur. The fair value of restricted stock awards is determined based on the market value of the Company’s shares on the grant date and the compensation expense is recognized on a straight-line basis during the service period of the respective grant.
Financial Derivatives	Derivative Instruments In the course of normal operations, the Company occasionally enters into contracts such as forward priced physical contracts for the purchase of raw materials that qualify for and are designated as normal purchase or normal sale contracts. Such contracts are exempted from the fair value accounting requirements and are accounted for at the time product is purchased or sold under the related contract. The Company does not engage in speculative transactions, nor does the Company hold or issue financial instruments for trading purposes.
Revenue Recognition	Revenue Recognition On January 1, 2018, we adopted the new accounting standard FASB ASC 606, Revenue from Contracts with Customers , and all the related amendments to all contracts using the retrospective method. The impact at adoption was not material to the consolidated financial statements. The new accounting policy provides results substantially consistent with prior revenue recognition policies. The Company recognizes revenue when it satisfies the performance obligation in its contracts. Most of the Company’s products are highly customized, cannot be resold to other customers and the cost of rework to be resold is not economical. The Company has a formal cancellation policy and generally does not accept returns on these units. As a result, many of the Company’s products do not have an alternative use and therefore, for these products we recognize revenue over the time it takes to produce the unit. For all other products that are part sales or standardized units, we satisfy the performance obligation when the title and risk of ownership pass to the customer, generally at time of shipment. Final sales prices are fixed based on purchase orders. Sales allowances and customer incentives are treated as reductions to sales and are provided for based on historical experiences and current estimates. Sales of our products are moderately seasonal with the peak period being July - November of each year. In addition, the Company presents revenues net of sales tax and net of certain payments to our independent manufacturer representatives (“Representatives”). Representatives are national companies that are in the business of providing HVAC units and other related products and services to customers. The end user customer orders a bundled group of products and services from the Representative and expects the Representative to fulfill the order. Only after the specifications are agreed to by the Representative and the customer, and the decision is made to use an AAON HVAC unit, will we receive notice of the order. We establish the amount we must receive for our HVAC unit (“minimum sales price”), but do not control the total order price that is negotiated by the Representative with the end user customer. We are responsible for billings and collections resulting from all sales transactions, including those initiated by our Representatives. The Representatives submit the total order price to us for invoicing and collection. The total order price includes our minimum sales price and an additional amount which may include both the Representatives’ fee and amounts due for additional products and services required by the customer. These additional products and services may include controls purchased from another manufacturer to operate the unit, start-up services, and curbs for supporting the unit (“Third Party Products”). All are associated with the purchase of a HVAC unit but may be provided by the Representative or another third party. The Company is under no obligation related to Third Party Products. The Representatives’ fee and Third Party Products amounts (“Due to Representatives”) are paid only after all amounts associated with the order are collected from the customer. The amount of payments to our representatives was $47.8 million , $51.8 million , and $55.0 million for each of the years ended December 31, 2018 , 2017 , and 2016 , respectively. The Company also sells extended warranties on parts for various lengths of time ranging from six months to 10 years. Revenue for these separately priced warranties is deferred and recognized on a straight-line basis over the separately priced warranty period.
Insurance Reserves	Insurance Reserves Under the Company’s insurance programs, coverage is obtained for significant liability limits as well as those risks required to be insured by law or contract. It is the policy of the Company to self-insure a portion of certain expected losses related primarily to workers’ compensation and medical liability. Provisions for losses expected under these programs are recorded based on the Company’s estimates of the aggregate liabilities for the claims incurred.
Product Warranties	Product Warranties A provision is made for the estimated cost of maintaining product warranties to customers at the time the product is sold based upon historical claims experience by product line. The Company records a liability and an expense for estimated future warranty claims based upon historical experience and management’s estimate of the level of future claims. Changes in the estimated amounts recognized in prior years are recorded as an adjustment to the liability and expense in the current year.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Because these estimates and assumptions require significant judgment, actual results could differ from those estimates and could have a significant impact on our results of operations, financial position and cash flows. We reevaluate our estimates and assumptions as needed, but at a minimum on a quarterly basis. The most significant estimates include, but are not limited to, the allowance for doubtful accounts, inventory reserves, warranty accrual, workers compensation accrual, medical insurance accrual, share-based compensation and income taxes. Actual results could differ materially from those estimates.
New Accounting Pronouncements	Changes to U.S. GAAP are established by the Financial Accounting Standards Board (“FASB”) in the form of accounting standards updates (“ASUs”) to the FASB’s Accounting Standards Codification. We consider the applicability and impact of all ASUs. ASUs not listed below were assessed and determined to be either not applicable or are expected to have minimal impact on our consolidated financial statements and notes thereto. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . The ASU will replace previous lease accounting guidance in U.S. GAAP. The ASU requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases. The ASU retains a distinction between finance leases and operating leases. The ASU is effective for the Company beginning January 1, 2019. The following ASUs have been issued in 2018 with the same effective dates and transition requirements: • ASU 2018-01, Land Easement Practical Expedient , which provides a relief from certain land easements held before the effective date. • ASU 2018-10, Leases: Codification Improvements , which provides clarification for various areas of Topic 842. • ASU 2018-11, Leases: Targeted Improvements , which provides clarification for several areas of Topic 842: comparative reporting requirements, an optional method of adoption (the transition method) and separating lease and non lease component for lessors. • ASU 2018-20, Leases: Narrow-Scope Improvement for Lessors , which provided clarification to lessors for sales taxes, variable payments and other costs. The Company historically does not enter into numerous or material lease agreements to support its manufacturing operations. The Company typically enters into lease agreements that are less than a year and for leases on assets such as warehouse vehicles and office equipment. The Company assumed a multi-year facility lease in the WattMaster acquisition. The Company has completed the process of determining our contracts to which this new guidance applies. The Company does not expect this new guidance to have a significant impact on the consolidated financial statements due to the non-material monetary amount of the total leased assets under the new applicable guidance. Furthermore, we have elected to apply the short-term lease accounting policy election to all short-term leases under the applicable guidance. Under the policy election the lessee does not recognize a short-term lease liability or right-of-use asset on its balance sheet. The Company will elect the transition method, which becomes effective upon the date of adoption of ASU 2016-02 discussed above. The transition method allows entities to initially apply the new leases standard at the adoption date (January 1, 2019) and recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We expect the cumulative-effect adjustments to the opening balance to be immaterial to the financial statements as a whole. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurements: Changes to the Disclosure Requirement for Fair Value Measurements . The ASU includes additional disclosure requirements for unrealized gains and losses for Level 3 fair value measurement and significant observable inputs used to develop Level 3 fair value measurements. The ASU is effective for the Company beginning after December 15, 2019. We do not expect ASU 2018-13 will have a material effect on our consolidated financial statements and notes thereto. In January 2017, the FASB issued ASU 2017-04, Intangibles-Goodwill and Other . The ASU simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. We will be required to perform our annual goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. In the event the carrying amount exceeds the reporting unit’s fair value, a goodwill impairment charge for the excess will be recorded (not exceeding the recorded amount of the reporting unit’s goodwill). The ASU is effective for the Company beginning April 1, 2020, and requires a prospective method of adoption, although early adoption is permitted for annual goodwill impairment tests performed on testing dates on or after January 1, 2017. We adopted this ASU effective January 1, 2018.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Amortized Cost and Estimated Fair Value of Investments Held to Maturity	The following summarizes the amortized cost and estimated fair value of our investments held to maturity at December 31, 2017 : Amortized Cost Gross Unrealized Gain Gross Unrealized (Loss) Fair Value December 31, 2017: Current assets: Investments held to maturity $ 6,077 $ — $ (6 ) $ 6,071 Non current assets: Investments held to maturity — — — — Total $ 6,077 $ — $ (6 ) $ 6,071
Estimated Useful Lives	Depreciation is computed using the straight-line method over the following estimated useful lives: Buildings 3-40 years Machinery and equipment 3-15 years Furniture and fixtures 3-7 years

Revenue Recognition (Tables)

Revenue Recognition (Tables)	12 Months Ended
	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	Disaggregated net sales by major source: Years Ending December 31, 2018 2017 2016 (in thousands) Rooftop Units $ 333,105 $ 317,414 $ 309,641 Condensing Units 18,282 19,276 13,987 Air Handlers 21,905 22,570 19,792 Outdoor Mechanical Rooms 2,408 3,238 4,515 Water Source Heat Pumps 14,660 9,911 5,835 Part Sales 26,732 20,756 20,374 Other 16,855 12,067 9,833 Net Sales $ 433,947 $ 405,232 $ 383,977 Other sales include freight, extended warranties and miscellaneous revenue. Disaggregated units sold by major source: Years Ending December 31, 2018 2017 2016 Rooftop Units 15,273 16,003 16,764 Condensing Units 2,007 2,252 1,639 Air Handlers 2,500 2,577 2,114 Outdoor Mechanical Rooms 38 64 65 Water Source Heat Pumps 5,334 2,485 316 Total Units 25,152 23,381 20,898

Business Combination (Tables)

Business Combination (Tables)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Schedule of Acquisition	The following table presents the allocation of the consideration paid to the assets acquired and liabilities assumed, based on their fair values, in the acquisition of WattMaster described above: Accounts receivable $ 1,082 Inventories 1,380 Property, plant and equipment 340 Intellectual property 700 Goodwill 3,229 Assumed current liabilities (354 ) Consideration paid $ 6,377

Accounts Receivable (Tables)

Accounts Receivable (Tables)	12 Months Ended
	Dec. 31, 2018
Receivables [Abstract]
Accounts Receivable	December 31, 2018 2017 (in thousands) Accounts receivable $ 54,342 $ 50,457 Less: Allowance for doubtful accounts (264 ) (119 ) Total, net $ 54,078 $ 50,338
Accounts Receivable (Allowance)	Years Ending December 31, 2018 2017 2016 Allowance for doubtful accounts: (in thousands) Balance, beginning of period $ 119 $ 90 $ 115 Provisions for losses on accounts receivable, net of adjustments 174 179 (25 ) Accounts receivable written off, net of recoveries (29 ) (150 ) — Balance, end of period $ 264 $ 119 $ 90

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2018
Inventory Disclosure [Abstract]
Inventories	The components of inventories and the related changes in the allowance for excess and obsolete inventories are as follows: December 31, 2018 2017 (in thousands) Raw materials $ 67,995 $ 57,784 Work in process 4,060 5,957 Finished goods 6,767 8,163 78,822 71,904 Less: Allowance for excess and obsolete inventories (1,210 ) (1,118 ) Total, net $ 77,612 $ 70,786
Inventories (Allowance)	Years Ending December 31, 2018 2017 2016 Allowance for excess and obsolete inventories: (in thousands) Balance, beginning of period $ 1,118 $ 1,382 $ 757 Provisions for excess and obsolete inventories 152 102 625 Inventories written off (60 ) (366 ) — Balance, end of period $ 1,210 $ 1,118 $ 1,382

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets	Our intangible assets consist of the following: December 31, 2018 2017 (in thousands) Intellectual property $ 700 $ — Less: Accumulated amortization (194 ) — Total, net $ 506 $ —
Schedule of Amortization Expense	Amortization expense recorded in cost of sales is as follows: Years Ending December 31, 2018 2017 2016 (in thousands) Amortization expense $ 194 $ — $ —

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Years Ending December 31, 2018 2017 2016 Supplemental disclosures: (in thousands) Interest paid $ 6 $ — $ — Income taxes paid, net 14,979 16,951 27,353 Non-cash investing and financing activities: Non-cash capital expenditures 481 832 270

Warranties (Tables)

Warranties (Tables)	12 Months Ended
	Dec. 31, 2018
Guarantees [Abstract]
Warranty	Changes in the warranty accrual are as follows: Years Ending December 31, 2018 2017 2016 Warranty accrual: (in thousands) Balance, beginning of period $ 10,483 $ 7,936 $ 8,469 Payments made (7,869 ) (8,686 ) (4,134 ) Provisions 9,669 11,233 3,601 Change in estimate (862 ) — — Balance, end of period $ 11,421 $ 10,483 $ 7,936 Warranty expense: $ 8,807 $ 11,233 $ 3,601

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued Liabilities	At December 31, accrued liabilities were comprised of the following: December 31, 2018 2017 (in thousands) Warranty $ 11,421 $ 10,483 Due to representatives 11,024 13,086 Payroll 4,182 4,456 Profit sharing 1,835 2,034 Workers' compensation 567 593 Medical self-insurance 1,207 725 Customer prepayments 2,367 2,838 Donations 150 588 Employee vacation time 3,173 2,688 Other 1,529 1,607 Total $ 37,455 $ 39,098

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Provision for Income Taxes	The provision (benefit) for income taxes consists of the following: Years Ending December 31, 2018 2017 2016 (in thousands) Current $ 10,518 $ 21,548 $ 25,790 Deferred 2,849 (1,554 ) 825 Total $ 13,367 $ 19,994 $ 26,615
Federal Statutory Income Tax Rate Reconciliation	The reconciliation of the federal statutory income tax rate to the effective income tax rate is as follows: Years Ending December 31, 2018 2017 2016 Federal statutory rate 21 % 35 % 35 % State income taxes, net of federal benefit 6 % 5 % 5 % Remeasurement of deferred taxes — % (6 )% — % Domestic manufacturing deduction — % (3 )% (3 )% Excess tax benefits (2 )% (3 )% (3 )% Other (1 )% (1 )% (1 )% 24 % 27 % 33 %
Deferred Tax Assets and Liabilities	The significant components of the Company’s deferred tax assets and liabilities are as follows: December 31, 2018 2017 (in thousands) Deferred income tax assets (liabilities): Accounts receivable and inventory reserves $ 401 $ 318 Warranty accrual 3,105 2,698 Other accruals 2,445 1,395 Share-based compensation 1,697 1,432 Donations 80 152 Other, net 851 698 Total deferred income tax assets 8,579 6,693 Property & equipment (19,405 ) (14,670 ) Total deferred income tax liabilities $ (19,405 ) $ (14,670 ) Net deferred income tax liabilities $ (10,826 ) $ (7,977 )

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock Option Assumptions	The following weighted average assumptions were used to determine the fair value of the stock options granted on the original grant date for expense recognition purposes for options granted during December 31, 2018 , 2017 , and 2016 using a Black Scholes-Merton Model: 2018 2017 2016 Director and Officers: Expected dividend yield $ 0.26 $ 0.26 $ 0.22 Expected volatility 29.73 % 30.81 % 41.19 % Risk-free interest rate 2.20 % 1.90 % 2.00 % Expected life (in years) 5.00 5.00 7.68 Employees: Expected dividend yield $ 0.26 $ 0.26 $ 0.25 Expected volatility 29.82 % 30.67 % 34.50 % Risk-free interest rate 2.51 % 1.89 % 1.73 % Expected life (in years) 5.00 5.00 5.69
Summary of Stock Options Outstanding	The following is a summary of stock options vested and exercisable as of December 31, 2018 : Weighted Average Weighted Range of Number Remaining Average Exercise of Contractual Exercise Intrinsic Prices Shares Life Price Value (in thousands) $5.67 - 32.80 456,223 5.72 $ 20.25 $ 6,757 $32.85 - 34.10 42,552 7.47 33.95 47 $34.15 - 42.94 17,202 8.30 35.19 7 Total 515,977 5.95 $ 21.88 $ 6,811 The following is a summary of stock options vested and exercisable as of December 31, 2017 : Weighted Average Weighted Range of Number Remaining Average Exercise of Contractual Exercise Intrinsic Prices Shares Life Price Value (in thousands) $4.54 - 22.76 424,130 4.36 $ 12.41 $ 10,303 $23.57 - 32.85 107,456 8.31 30.10 709 $32.90 - 37.30 25,725 9.19 34.07 68 Total 557,311 5.35 $ 16.82 $ 11,080 The following is a summary of stock options vested and exercisable as of December 31, 2016 : Weighted Average Weighted Range of Number Remaining Average Exercise of Contractual Exercise Intrinsic Prices Shares Life Price Value (in thousands) $4.54 - 20.92 338,308 4.75 $ 8.03 $ 8,465 $20.96 - 26.50 71,928 8.56 22.50 759 Total 410,236 5.42 $ 10.57 $ 9,224
Summary of Stock Option Activity	A summary of option activity under the plans is as follows: Weighted Average Exercise Options Shares Price Outstanding at December 31, 2017 1,567,109 $ 25.27 Granted 1,480,490 34.49 Exercised (282,598 ) 17.64 Forfeited or Expired (319,152 ) 32.84 Outstanding at December 31, 2018 2,445,849 $ 30.77 Exercisable at December 31, 2018 515,977 $ 21.89
Summary of Unvested Restricted Stock Awards	A summary of the unvested restricted stock awards is as follows: Weighted Average Grant date Restricted stock Shares Fair Value Unvested at December 31, 2017 341,800 $ 25.52 Granted 112,075 32.20 Vested (124,508 ) 23.61 Forfeited (36,917 ) 28.37 Unvested at December 31, 2018 292,450 $ 28.54
Summary of Grant Date Fair Value of Awards During Period	2018 2017 2016 Grant date fair value of awards during the period: (in thousands) Options $ 12,932 $ 3,699 $ 6,102 Restricted stock 3,609 4,217 3,147 Total $ 16,541 $ 7,916 $ 9,249
Summary of Share-Based Compensation Expense	2018 2017 2016 Share-based compensation expense: (in thousands) Options $ 4,181 $ 2,904 $ 1,681 Restricted stock 3,193 3,554 2,676 Total $ 7,374 $ 6,458 $ 4,357
Summary of Income Tax Benefit Related to Share-Based Compensation	2018 2017 2016 Income tax benefit related to share-based compensation: (in thousands) Options $ 980 $ 1,413 $ 1,610 Restricted stock 353 1,051 458 Total $ 1,333 $ 2,464 $ 2,068

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Share Repurchases	Our repurchase activity is as follows: 2018 2017 2016 Program Shares Total $ $ per share Shares Total $ $ per share Shares Total $ $ per share Open market 252,272 $ 8,373,698 $ 33.19 8,676 $ 283,654 $ 32.69 165,598 $ 4,440,658 $ 26.82 401(k) 497,753 18,472,442 37.11 467,580 16,336,084 34.94 540,501 14,875,850 27.52 Directors & employees 33,751 1,096,625 32.49 45,878 1,614,425 35.19 30,072 823,446 27.38 Total 783,776 $ 27,942,765 $ 35.65 522,134 $ 18,234,163 $ 34.92 736,171 $ 20,139,954 $ 27.36 Inception to Date Program Shares Total $ $ per share Open market 4,095,767 $ 69,605,813 $ 16.99 401(k) 7,047,776 100,541,247 14.27 Directors & employees 1,953,261 18,374,658 9.41 Total 13,096,804 $ 188,521,718 $ 14.39
Schedule of Dividends	Our recent dividends are as follows: Declaration Date Record Date Payment Date Dividend per Share May 24, 2016 June 10, 2016 July 1, 2016 $0.11 November 9, 2016 December 2, 2016 December 23, 2016 $0.13 May 16, 2017 June 9, 2017 July 7, 2017 $0.13 November 7, 2017 November 30, 2017 December 21, 2017 $0.13 May 18, 2018 June 8, 2018 July 6, 2018 $0.16 November 8, 2018 November 29, 2018 December 20, 2018 $0.16

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share Table	The following table sets forth the computation of basic and diluted earnings per share: 2018 2017 2016 Numerator: (in thousands, except share and per share data) Net income $ 42,572 $ 54,498 $ 53,376 Denominator: Basic weighted average shares 52,284,616 52,572,496 52,924,398 Effect of dilutive stock options and restricted stock 383,323 506,238 525,356 Diluted weighted average shares 52,667,939 53,078,734 53,449,754 Earnings per share: Basic $ 0.81 $ 1.04 $ 1.01 Dilutive $ 0.81 $ 1.03 $ 1.00 Anti-dilutive shares: Shares 1,920,313 785,825 469,603

Related Parties (Tables)

Related Parties (Tables)	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Schedule of Related Party Transactions	Following is a summary of transactions and balances with affiliates: Years Ending December 31, 2018 2017 2016 (in thousands) Sales to affiliates $ 1,442 $ 1,579 $ 1,671 Payments to affiliates 342 432 697 December 31, 2018 2017 (in thousands) Due from affiliates $ 79 $ 9 Due to affiliates — —

Quarterly Results (Unaudited) (

Quarterly Results (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results of Operations	The following is a summary of the quarterly results of operations for the years ending December 31, 2018 and 2017 : Quarter First Second Third Fourth (in thousands, except per share data) 2018 Net sales $ 99,082 $ 109,588 $ 112,937 $ 112,340 Gross profit 15,390 27,585 32,763 27,795 Net income 4,260 11,691 14,085 12,536 Earnings per share: Basic $ 0.08 $ 0.22 $ 0.27 $ 0.24 Diluted $ 0.08 $ 0.22 $ 0.27 $ 0.24 2017 Net sales $ 86,078 $ 101,326 $ 113,668 $ 104,160 Gross profit 24,986 31,678 35,658 31,075 Net income 10,217 13,794 14,717 15,770 Earnings per share: Basic $ 0.19 $ 0.26 $ 0.28 $ 0.30 Diluted $ 0.19 $ 0.26 $ 0.28 $ 0.30

Segments (Tables)

Segments (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	The following table summarizes certain financial data related to our segments. Transactions between segments are recorded based on prices negotiated between the segments. Sales of units represents the selling price of our units plus freight and other miscellaneous charges less any returns and allowances. Parts includes sales of purchased and fabricated parts including our coils along with the related freight and less any returns and allowances. The “Other” category in the table below includes certain sales cost and expenses that are not allocated to the reportable segments. Asset information by segment is not easily identifiable or reviewed by the chief operating decision maker. As such, this information is not included below. Years Ending December 31, 2018 2017 2016 (in thousands) Sales Units 406,331 384,853 363,666 Parts - External 28,456 22,050 21,692 Parts - Inter-segment 29,385 29,293 25,406 Other (840 ) (1,671 ) (1,381 ) Eliminations (29,385 ) (29,293 ) (25,406 ) Net sales 433,947 405,232 383,977 Gross Profit Units 108,214 128,571 120,940 Parts - External 13,215 9,377 9,967 Parts - Inter-segment 865 426 (105 ) Other (17,896 ) (14,551 ) (12,827 ) Eliminations (865 ) (426 ) 105 Net gross profit 103,533 123,397 118,080

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2018USD ($)customer	Dec. 31, 2017USD ($)customer	Dec. 31, 2016USD ($)customer
Schedule of Accounting Policies [Line Items]
Certificates of deposit	$ 0	$ 2,880,000
Investments held to maturity	0	6,077,000
Research and development costs	13,500,000	13,000,000	$ 12,000,000
Advertising expense	800,000	1,700,000	1,400,000
Payments to representatives	$ 47,800,000	51,800,000	55,000,000
Extended product warranties, minimum length	6 months
Extended product warranties, maximum length	10 years
Shipping and Handling
Schedule of Accounting Policies [Line Items]
Cost of sales	$ 12,600,000	$ 11,400,000	$ 10,300,000
Foreign Sales Revenue, Net
Schedule of Accounting Policies [Line Items]
Concentration risk, percentage	3.00%	4.00%	4.00%
Sales Revenue, Net
Schedule of Accounting Policies [Line Items]
Number of major customers | customer	1	1	1
Accounting for More Than 5% of Accounts Receivable
Schedule of Accounting Policies [Line Items]
Concentration risk, percentage	5.00%	5.00%
Number of major customers	0	0

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Investments Held to Maturity (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Gain (Loss) on Securities [Line Items]
Amortized Cost	$ 0	$ 6,077,000
Gross Unrealized Gain		0
Gross Unrealized (Loss)		(6,000)
Fair Value		6,071,000
Current Assets
Gain (Loss) on Securities [Line Items]
Amortized Cost		6,077,000
Gross Unrealized Gain		0
Gross Unrealized (Loss)		(6,000)
Fair Value		6,071,000
Non Current Assets
Gain (Loss) on Securities [Line Items]
Amortized Cost		0
Gross Unrealized Gain		0
Gross Unrealized (Loss)		0
Fair Value		$ 0

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Estimated Useful Lives (Details)	12 Months Ended
	Dec. 31, 2018
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	40 years
Machinery and Equipment | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Machinery and Equipment | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Furniture and Fixtures | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Furniture and Fixtures | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years

Revenue Recognition (Details)

Revenue Recognition (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)unit	Dec. 31, 2017USD ($)unit	Dec. 31, 2016USD ($)unit
Disaggregation of Revenue [Line Items]
Net sales	$ 433,947	$ 405,232	$ 383,977
Total Units | unit	25,152,000	23,381,000	20,898,000
Rooftop Units
Disaggregation of Revenue [Line Items]
Net sales	$ 333,105	$ 317,414	$ 309,641
Total Units | unit	15,273,000	16,003,000	16,764,000
Condensing Units
Disaggregation of Revenue [Line Items]
Net sales	$ 18,282	$ 19,276	$ 13,987
Total Units | unit	2,007,000	2,252,000	1,639,000
Air Handlers
Disaggregation of Revenue [Line Items]
Net sales	$ 21,905	$ 22,570	$ 19,792
Total Units | unit	2,500,000	2,577,000	2,114,000
Outdoor Mechanical Rooms
Disaggregation of Revenue [Line Items]
Net sales	$ 2,408	$ 3,238	$ 4,515
Total Units | unit	38,000	64,000	65,000
Water Source Heat Pumps
Disaggregation of Revenue [Line Items]
Net sales	$ 14,660	$ 9,911	$ 5,835
Total Units | unit	5,334,000	2,485,000	316,000
Part Sales
Disaggregation of Revenue [Line Items]
Net sales	$ 26,732	$ 20,756	$ 20,374
Other
Disaggregation of Revenue [Line Items]
Net sales	$ 16,855	$ 12,067	$ 9,833

Business Combination (Details)

Business Combination (Details) - USD ($) $ in Thousands	Feb. 28, 2018	May 31, 2018	Dec. 31, 2018	Mar. 01, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Working capital settlement paid		$ 400
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Goodwill			$ 3,229		$ 0
WattMaster
Business Acquisition [Line Items]
Payments to acquire businesses	$ 6,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract]
Accounts receivable				$ 1,082
Inventories				1,380
Property, plant and equipment				340
Intellectual property				700
Goodwill				3,229
Assumed current liabilities				(354)
Consideration paid				$ 6,377

Accounts Receivable (Balance) (

Accounts Receivable (Balance) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Receivables [Abstract]
Accounts receivable	$ 54,342	$ 50,457
Less: Allowance for doubtful accounts	(264)	(119)
Total, net	$ 54,078	$ 50,338

Accounts Receivable (Allowance)

Accounts Receivable (Allowance) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for doubtful accounts:
Balance, beginning of period	$ 119	$ 90	$ 115
Provisions for losses on accounts receivable, net of adjustments	174	179	(25)
Accounts receivable written off, net of recoveries	(29)	(150)	0
Balance, end of period	$ 264	$ 119	$ 90

Inventories - Components (Detai

Inventories - Components (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Inventory Disclosure [Abstract]
Raw materials	$ 67,995	$ 57,784
Work in process	4,060	5,957
Finished goods	6,767	8,163
Inventory, gross	78,822	71,904
Less: Allowance for excess and obsolete inventories	(1,210)	(1,118)	$ (1,382)	$ (757)
Total, net	$ 77,612	$ 70,786

Inventories - Allowance (Detail

Inventories - Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allowance for excess and obsolete inventories:
Balance, beginning of period	$ 1,118	$ 1,382	$ 757
Provisions for excess and obsolete inventories	152	102	625
Inventories written off	(60)	(366)	0
Balance, end of period	$ 1,210	$ 1,118	$ 1,382

Intangible Assets (Details)

Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Intellectual property
Intellectual property	$ 700	$ 0
Less: Accumulated amortization	(194)	0
Total, net	506	0
Amortization expense	$ 194	$ 0	$ 0

Note Receivable (Details)

Note Receivable (Details) $ in Thousands, $ in Millions	Sep. 30, 2010CAD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Note Receivable [Abstract]
Note receivable	$ 1.1	$ 598	$ 678
Term	15 years
Interest rate	4.00%
Balloon payment on note receivable	$ 0.6
Balloon payment due date		October 2,025

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental disclosures:
Interest paid	$ 6	$ 0	$ 0
Income taxes paid, net	14,979	16,951	27,353
Non-cash investing and financing activities:
Non-cash capital expenditures	$ 481	$ 832	$ 270

Warranties - Narrative (Details

Warranties - Narrative (Details)	12 Months Ended
	Dec. 31, 2018
Guarantees [Abstract]
Product warranty accrual, minimum length	18 months
Product warranty accrual, maximum length	25 years

Warranties - Changes in Warrant

Warranties - Changes in Warrants (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Warranty accrual:
Balance, beginning of period	$ 10,483	$ 7,936	$ 8,469
Payments made	(7,869)	(8,686)	(4,134)
Provisions	9,669	11,233	3,601
Change in estimate	(862)	0	0
Balance, end of period	11,421	10,483	7,936
Warranty expense	$ 8,807	$ 11,233	$ 3,601

Accrued Liabilities (Details)

Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Warranty	$ 11,421	$ 10,483
Due to representatives	11,024	13,086
Payroll	4,182	4,456
Profit sharing	1,835	2,034
Workers' compensation	567	593
Medical self-insurance	1,207	725
Customer prepayments	2,367	2,838
Donations	150	588
Employee vacation time	3,173	2,688
Other	1,529	1,607
Total	$ 37,455	$ 39,098

Revolving Credit Facility (Deta

Revolving Credit Facility (Details)	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Line of Credit Facility [Line Items]
Actual net worth for compliance	$ 247,500,000
Minimum net worth required for compliance	$ 175,000,000
Ratio of total liability to net worth	0.2
Maximum ratio of total liability to net worth for compliance	2
Revolving Credit Facility
Line of Credit Facility [Line Items]
Credit facility maximum borrowings	$ 30,000,000
Standby letter of credit	1,300,000
Borrowings available under the revolving credit facility	$ 28,700,000
Frequency of periodic payments	monthly
Fees associated with unused portion of committed amount	$ 0
Borrowings outstanding under revolving credit facility	$ 0	$ 0
Weighted average interest rate	4.20%	3.50%
Revolving Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Stated percentage	2.00%

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018USD ($)
Income Tax Disclosure [Abstract]
Doubling bonus depreciation for five years, percent	100.00%	100.00%
Tax Cuts and Jobs Act of 2017, income tax benefit	$ 4.4
Tax Cuts and Jobs Act of 2017, Change in tax rate, bonus depreciation	3.2
Deduction to effective income tax rate, percent		3.00%
Executive compensation limitation	$ 1	$ 1

Income Taxes - Provision for In

Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current	$ 10,518	$ 21,548	$ 25,790
Deferred	2,849	(1,554)	825
Total	$ 13,367	$ 19,994	$ 26,615

Income Taxes - Federal Statutor

Income Taxes - Federal Statutory Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	35.00%	35.00%
State income taxes, net of federal benefit	6.00%	5.00%	5.00%
Effective Income Tax Rate Reconciliation, Remeasurement of Deferred Taxes, Percent	(0.00%)	6.00%	(0.00%)
Domestic manufacturing deduction	(0.00%)	(3.00%)	(3.00%)
Excess tax benefits	(2.00%)	(3.00%)	(3.00%)
Other	(1.00%)	(1.00%)	(1.00%)
Total	24.00%	27.00%	33.00%

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Net long-term deferred assets and (liabilities) relating to:
Accounts receivable and inventory reserves	$ 401	$ 318
Warranty accrual	3,105	2,698
Other accruals	2,445	1,395
Share-based compensation	1,697	1,432
Donations	80	152
Other, net	851	698
Total deferred income tax assets	8,579	6,693
Property & equipment	(19,405)	(14,670)
Total deferred income tax liabilities	(19,405)	(14,670)
Net deferred income tax liabilities	$ 10,826	$ 7,977

Share-Based Compensation - Narr

Share-Based Compensation - Narrative (Details) - USD ($) $ in Thousands	May 24, 2016	May 22, 2007	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 15, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock authorized to be issued under plan (in shares)	6,400,000
Unrecognized pre-tax compensation cost			$ 14,300
Weighted average recognition period (in years)			2 years 3 months 15 days
Total intrinsic value of options exercised during period			$ 5,400	$ 4,500	$ 4,900
Cash received from options exercised during period			4,987	$ 2,259	$ 2,063
2007 Long-Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock authorized to be issued under plan (in shares)	400,000	3,300,000
Award vesting period		5 years
Exercise price of shares granted may not be less than fair market value (percentage)		100.00%
2007 Long-Term Incentive Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized pre-tax compensation cost			$ 6,100
Weighted average recognition period (in years)			1 year 10 months 2 days
Annual vesting, percentage			20.00%
2016 Long-Term Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock authorized to be issued under plan (in shares)	3,400,000					2,600,000
Exercise price of shares granted may not be less than fair market value (percentage)	100.00%

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Assumptions (Details) - 2007 Long-Term Incentive Plan	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Director and Officers
Expected dividend yield	26.00%	26.00%	22.00%
Expected volatility	29.73%	30.81%	41.19%
Risk-free interest rate	2.20%	1.90%	2.00%
Expected life (in years)	5 years	5 years	7 years 8 months 5 days
Employees
Expected dividend yield	26.00%	26.00%	25.00%
Expected volatility	29.82%	30.67%	34.50%
Risk-free interest rate	2.51%	1.89%	1.73%
Expected life (in years)	5 years	5 years	5 years 8 months 9 days

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Stock Options Outstanding (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of shares vested and exercisable	515,977	557,311	410,236
Options vested and exercisable weighted average remaining contractual life	5 years 11 months 12 days	5 years 4 months 6 days	5 years 5 months 1 day
Options vested and exercisable weighted average exercise price	$ 21.88	$ 16.82	$ 10.57
Options vested and exercisable intrinsic value	$ 6,811	$ 11,080	$ 9,224
$5.67 - 32.80
Range of exercise prices, lower range	$ 5.67
Range of exercise prices, upper range	$ 32.80
Number of shares vested and exercisable	456,223
Options vested and exercisable weighted average remaining contractual life	5 years 8 months 19 days
Options vested and exercisable weighted average exercise price	$ 20.25
Options vested and exercisable intrinsic value	$ 6,757
$32.85 - 34.10
Range of exercise prices, lower range	$ 32.85
Range of exercise prices, upper range	$ 34.10
Number of shares vested and exercisable	42,552
Options vested and exercisable weighted average remaining contractual life	7 years 5 months 19 days
Options vested and exercisable weighted average exercise price	$ 33.95
Options vested and exercisable intrinsic value	$ 47
$34.15 - 42.94
Range of exercise prices, lower range	$ 34.15
Range of exercise prices, upper range	$ 42.94
Number of shares vested and exercisable	17,202
Options vested and exercisable weighted average remaining contractual life	8 years 3 months 18 days
Options vested and exercisable weighted average exercise price	$ 35.19
Options vested and exercisable intrinsic value	$ 7
$4.54 - 22.76
Range of exercise prices, lower range		$ 4.54
Range of exercise prices, upper range		$ 22.76
Number of shares vested and exercisable		424,130
Options vested and exercisable weighted average remaining contractual life		4 years 4 months 10 days
Options vested and exercisable weighted average exercise price		$ 12.41
Options vested and exercisable intrinsic value		$ 10,303
$23.57 - 32.85
Range of exercise prices, lower range		$ 23.57
Range of exercise prices, upper range		$ 32.85
Number of shares vested and exercisable		107,456
Options vested and exercisable weighted average remaining contractual life		8 years 3 months 22 days
Options vested and exercisable weighted average exercise price		$ 30.10
Options vested and exercisable intrinsic value		$ 709
$32.90 - 37.30
Range of exercise prices, lower range		$ 32.90
Range of exercise prices, upper range		$ 37.30
Number of shares vested and exercisable		25,725
Options vested and exercisable weighted average remaining contractual life		9 years 2 months 9 days
Options vested and exercisable weighted average exercise price		$ 34.07
Options vested and exercisable intrinsic value		$ 68
$4.54 - 20.92
Range of exercise prices, lower range			$ 4.54
Range of exercise prices, upper range			$ 20.92
Number of shares vested and exercisable			338,308
Options vested and exercisable weighted average remaining contractual life			4 years 9 months
Options vested and exercisable weighted average exercise price			$ 8.03
Options vested and exercisable intrinsic value			$ 8,465
$20.96 - 26.50
Range of exercise prices, lower range			$ 20.96
Range of exercise prices, upper range			$ 26.50
Number of shares vested and exercisable			71,928
Options vested and exercisable weighted average remaining contractual life			8 years 6 months 22 days
Options vested and exercisable weighted average exercise price			$ 22.50
Options vested and exercisable intrinsic value			$ 759

Share-Based Compensation - Su_3

Share-Based Compensation - Summary of Stock Option Activity (Details)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Shares
Outstanding, beginning of period (in shares) | shares	1,567,109
Granted (in shares) | shares	1,480,490
Exercised (in shares) | shares	(282,598)
Forfeited or Expired (in shares) | shares	(319,152)
Outstanding, end of period (in shares) | shares	2,445,849
Exercisable, end of period (in shares) | shares	515,977
Weighted Average Exercise Price
Outstanding, beginning of period (weighted average exercise price) | $ / shares	$ 25.27
Granted (weighted average exercise price) | $ / shares	34.49
Exercised (weighted average exercise price) | $ / shares	17.64
Forfeited or Expired (weighted average exercise price) | $ / shares	32.84
Outstanding, end of period (weighted average exercise price) | $ / shares	30.77
Exercisable, end of period (weighted average exercise price) | $ / shares	$ 21.89

Share-Based Compensation - Su_4

Share-Based Compensation - Summary of Unvested Restricted Stock Awards (Details)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested, beginning of period (in shares) | shares	341,800
Granted (in shares) | shares	112,075
Vested (in shares) | shares	(124,508)
Forfeited (in shares) | shares	(36,917)
Unvested, end of period (in shares) | shares	292,450
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Unvested, beginning of period (weighted average grant date fair value) | $ / shares	$ 25.52
Granted (weighted average grant date fair value) | $ / shares	32.20
Vested (weighted average grant date fair value) | $ / shares	23.61
Forfeited (weighted average grant date fair value) | $ / shares	28.37
Unvested, end of period (weighted average grant date fair value) | $ / shares	$ 28.54

Share-Based Compensation - Su_5

Share-Based Compensation - Summary of Grant Date Fair Value of Awards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options	$ 12,932	$ 3,699	$ 6,102
Restricted stock	3,609	4,217	3,147
Total	$ 16,541	$ 7,916	$ 9,249

Share-Based Compensation - Su_6

Share-Based Compensation - Summary of Share-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options	$ 4,181	$ 2,904	$ 1,681
Restricted stock	3,193	3,554	2,676
Total	$ 7,374	$ 6,458	$ 4,357

Share-Based Compensation - Su_7

Share-Based Compensation - Summary of Income Tax Benefit Related to Share-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Options	$ 980	$ 1,413	$ 1,610
Restricted stock	353	1,051	458
Total	$ 1,333	$ 2,464	$ 2,068

Employee Benefits (Details)

Employee Benefits (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Definedcontributionemployeeautomaticcontributionpercentag	6.00%
Employer matching contributions	$ 8,100,000	$ 6,100,000	$ 5,900,000
Administrative expenses	$ 0	0	40,000
Profits sharing, percent of pre-tax profit paid to eligible employees on quarterly basis	10.00%
Profit sharing expense	$ 6,200,000	$ 8,400,000	$ 9,000,000
Effective January 1, 2016
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent of match	175.00%
Maximum annual contributions per employee, percent	6.00%

Shareholders' Equity (Details)

Shareholders' Equity (Details)	Nov. 08, 2018$ / shares	May 18, 2018$ / shares	Nov. 07, 2017$ / shares	May 16, 2017$ / shares	Nov. 09, 2016$ / shares	May 24, 2016USD ($)$ / shares	Jul. 16, 2014	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	May 15, 2018USD ($)	Jun. 02, 2016USD ($)shares	May 19, 2015shares
Schedule of Shareholders' Equity [Line Items]
Stock repurchased during period (in shares) | shares								783,776	522,134	736,171			13,096,804
Aggregate price of shares repurchased since inception | $								$ 27,942,765	$ 18,234,163	$ 20,139,954			$ 188,521,718
Average price of shares repurchased since inception (per share) | $ / shares								$ 35.65	$ 34.92	$ 27.36			$ 14.39
Dividends declared (per share) | $ / shares								$ 0.32	$ 0.26	$ 0.24
Stock split, conversion ratio							1.5
Cash dividends paid | $								$ 16,700,000	$ 13,700,000	$ 12,700,000
Regular Semi-Annual Dividend
Schedule of Shareholders' Equity [Line Items]
Dividends declared (per share) | $ / shares	$ 0.16	$ 0.16	$ 0.13	$ 0.13	$ 0.13	$ 0.11
Open market
Schedule of Shareholders' Equity [Line Items]
Stock repurchase program amount authorized (in shares) | shares															2,000,000	5,700,000
Stock repurchase program amount authorized, value | $						$ 25,000,000								$ 15,000,000	$ 25,000,000
Stock repurchased during period (in shares) | shares								252,272	8,676	165,598	4,095,767
Aggregate price of shares repurchased since inception | $								$ 8,373,698	$ 283,654	$ 4,440,658	$ 69,605,813
Average price of shares repurchased since inception (per share) | $ / shares								$ 33.19	$ 32.69	$ 26.82	$ 16.99
401(k)
Schedule of Shareholders' Equity [Line Items]
Stock repurchased during period (in shares) | shares								497,753	467,580	540,501			7,047,776
Aggregate price of shares repurchased since inception | $								$ 18,472,442	$ 16,336,084	$ 14,875,850			$ 100,541,247
Average price of shares repurchased since inception (per share) | $ / shares								$ 37.11	$ 34.94	$ 27.52			$ 14.27
Directors & employees
Schedule of Shareholders' Equity [Line Items]
Stock repurchased during period (in shares) | shares								33,751	45,878	30,072		1,953,261
Aggregate price of shares repurchased since inception | $								$ 1,096,625	$ 1,614,425	$ 823,446		$ 18,374,658
Average price of shares repurchased since inception (per share) | $ / shares								$ 32.49	$ 35.19	$ 27.38		$ 9.41

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Dec. 31, 2018USD ($)contract
Commitments and Contingencies Disclosure [Abstract]
Number of contracts | contract	1
Contractual obligation | $	$ 2.2

Earnings Per Share (Details)

Earnings Per Share (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
Earnings Per Share [Abstract]
Net income	$ 12,536	$ 14,085	$ 11,691	$ 4,260	$ 15,770	$ 14,717	$ 13,794	$ 10,217	$ 42,572	$ 54,498	$ 53,376
Basic weighted average shares									52,284,616	52,572,496	52,924,398
Effect of dilutive stock options and restricted stock									383,323	506,238	525,356
Diluted weighted average shares									52,667,939	53,078,734	53,449,754
Basic (usd per share)	$ 0.24	$ 0.27	$ 0.22	$ 0.08	$ 0.30	$ 0.28	$ 0.26	$ 0.19	$ 0.81	$ 1.04	$ 1.01
Diluted (usd per share)	$ 0.24	$ 0.27	$ 0.22	$ 0.08	$ 0.30	$ 0.28	$ 0.26	$ 0.19	$ 0.81	$ 1.03	$ 1
Anti-dilutive shares (in shares)									1,920,313	785,825	469,603

Related Parties (Details)

Related Parties (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Related Party Transactions [Abstract]
Sales to affiliates	$ 1,442	$ 1,579	$ 1,671
Payments to affiliates	342	432	$ 697
Due from affiliates	79	9
Due to affiliates	$ 0	$ 0

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Millions	Jan. 31, 2019	Feb. 25, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Granted (in shares)			112,075
Granted (in shares)			1,480,490
Subsequent Event | Open Market
Subsequent Event [Line Items]
Stock repurchased during period (in shares)		5,799
Stock repurchased during period		$ 0.2
Subsequent Event | 401(k) Savings and Investment Plan
Subsequent Event [Line Items]
Stock repurchased during period (in shares)		58,386
Stock repurchased during period		$ 2.2
Subsequent Event | Restricted Stock
Subsequent Event [Line Items]
Granted (in shares)	77,434
Subsequent Event | Stock Option | Non-Officer Employees
Subsequent Event [Line Items]
Granted (in shares)	840,000

Quarterly Results (Unaudited)_2

Quarterly Results (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
Disaggregation of Revenue [Line Items]
Net sales									$ 433,947	$ 405,232	$ 383,977
Gross profit	$ 27,795	$ 32,763	$ 27,585	$ 15,390	$ 31,075	$ 35,658	$ 31,678	$ 24,986	103,533	123,397	118,080
Net income	$ 12,536	$ 14,085	$ 11,691	$ 4,260	$ 15,770	$ 14,717	$ 13,794	$ 10,217	$ 42,572	$ 54,498	$ 53,376
Earnings per share:
Basic (usd per share)	$ 0.24	$ 0.27	$ 0.22	$ 0.08	$ 0.30	$ 0.28	$ 0.26	$ 0.19	$ 0.81	$ 1.04	$ 1.01
Diluted (usd per share)	$ 0.24	$ 0.27	$ 0.22	$ 0.08	$ 0.30	$ 0.28	$ 0.26	$ 0.19	$ 0.81	$ 1.03	$ 1
Product
Disaggregation of Revenue [Line Items]
Net sales	$ 112,340	$ 112,937	$ 109,588	$ 99,082	$ 104,160	$ 113,668	$ 101,326	$ 86,078	$ 433,947	$ 405,232	$ 383,977

Segments (Details)

Segments (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 [Line Items]
Net sales									$ 433,947	$ 405,232	$ 383,977
Gross profit	$ 27,795	$ 32,763	$ 27,585	$ 15,390	$ 31,075	$ 35,658	$ 31,678	$ 24,986	103,533	123,397	118,080
Operating Segments | Units
Segment Reporting Information [Line Items]
Net sales									406,331	384,853	363,666
Gross profit									108,214	128,571	120,940
Operating Segments | Parts
Segment Reporting Information [Line Items]
Net sales									28,456	22,050	21,692
Gross profit									13,215	9,377	9,967
Other
Segment Reporting Information [Line Items]
Net sales									(840)	(1,671)	(1,381)
Gross profit									(17,896)	(14,551)	(12,827)
Inter-segment
Segment Reporting Information [Line Items]
Net sales									29,385	29,293	25,406
Gross profit									$ 865	$ 426	$ (105)