ADTRAN (ADTN) 10-K 26 Feb 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 24, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	ADTN
Entity Registrant Name	ADTRAN, Inc.
Entity Central Index Key	0000926282
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Small Business	false
ICFR Auditor Attestation Flag	true
Entity Common Stock, Shares Outstanding		48,337,561
Entity Public Float			$ 520,493,715
Entity Interactive Data Current	Yes
Entity File Number	000-24612
Entity Tax Identification Number	63-0918200
Entity Address, Address Line One	901 Explorer Boulevard
Entity Address, City or Town	Huntsville
Entity Address, State or Province	AL
Entity Address, Postal Zip Code	35806-2807
City Area Code	256
Local Phone Number	963-8000
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, Par Value $0.01
Security Exchange Name	NASDAQ
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the Proxy Statement for the Annual Meeting of Stockholders to be held on May 12, 2021 are incorporated herein by reference in Part III.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current Assets
Cash and cash equivalents	$ 60,161	$ 73,773
Restricted cash	18
Short-term investments (includes $1,731 and $5,201 of available-for-sale securities as of December 31, 2020 and 2019, respectively, reported at fair value)	3,131	33,243
Accounts receivable, less allowance for doubtful accounts of $38 as of December 31, 2020 and 2019	98,827	90,531
Other receivables	21,531	16,566
Inventory, net	125,457	98,305
Prepaid expenses and other current assets	8,293	7,892
Total Current Assets	317,418	320,310
Property, plant and equipment, net	62,399	68,086
Deferred tax assets, net	9,869	7,561
Goodwill	6,968	6,968
Intangibles, net	23,470	27,821
Other non-current assets	25,425	19,883
Long-term investments (includes $43,385 and $32,459 of available-for-sale securities as of December 31, 2020 and 2019, respectively, reported at fair value)	80,130	94,489
Total Assets	525,679	545,118
Current Liabilities
Accounts payable	49,929	44,870
Bonds payable		24,600
Unearned revenue	14,092	11,963
Accrued expenses and other liabilities	13,609	13,876
Accrued wages and benefits	15,262	13,890
Income tax payable, net	1,301	3,512
Total Current Liabilities	94,193	112,711
Non-current unearned revenue	6,888	6,012
Pension liability	18,664	15,886
Deferred compensation liability	25,866	21,698
Other non-current liabilities	7,124	8,385
Total Liabilities	152,735	164,692
Commitments and contingencies (see Note 17)
Stockholders' Equity
Common stock, par value $0.01 per share; 200,000 shares authorized; 79,652 shares issued and 48,241 shares outstanding as of December 31, 2020 and 79,652 shares issued and 48,020 shares outstanding as of December 31, 2019	797	797
Additional paid-in capital	281,466	274,632
Accumulated other comprehensive loss	(11,639)	(16,417)
Retained earnings	781,813	806,702
Less treasury stock at cost: 31,280 and 31,638 shares as of December 31, 2020 and 2019, respectively	(679,493)	(685,288)
Total Stockholders' Equity	372,944	380,426
Total Liabilities and Stockholders' Equity	$ 525,679	$ 545,118

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Short term investments, available-for-sale securities at fair value	$ 1,731	$ 5,201
Allowance for doubtful accounts	38	38
Long Term Investments, available-for-sale securities Fair Value	$ 43,385	$ 32,459
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	79,652,000	79,652,000
Common stock, shares outstanding	48,241,000	48,020,000
Treasury stock, shares	31,280,000	31,638,000

Consolidated Statements of Inco

Consolidated Statements of Income (Loss) - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Sales
Total Sales	$ 506,510,000	$ 530,061,000	$ 529,277,000
Cost of Sales
Total Cost of Sales	288,959,000	310,894,000	325,712,000
Gross Profit	217,551,000	219,167,000	203,565,000
Selling, general and administrative expenses	113,972,000	130,288,000	124,440,000
Research and development expenses	113,287,000	126,200,000	124,547,000
Asset impairments	65,000	3,872,000	0
Gain on contingency		(1,230,000)
Operating Loss	(9,773,000)	(39,963,000)	(45,422,000)
Interest and dividend income	1,936,000	2,765,000	4,026,000
Interest expense	(5,000)	(511,000)	(533,000)
Net investment gain (loss)	4,850,000	11,434,000	(4,050,000)
Other income (expense), net	(3,254,000)	1,498,000	1,286,000
Gain on bargain purchase of a business			11,322,000
Loss Before Income Taxes	(6,246,000)	(24,777,000)	(33,371,000)
Income tax (expense) benefit	8,624,000	(28,205,000)	14,029,000
Net Income (Loss)	$ 2,378,000	$ (52,982,000)	$ (19,342,000)
Weighted average shares outstanding – basic	47,996	47,836	47,880
Weighted average shares outstanding – diluted	48,288	47,836	47,880
Earnings (loss) per common share – basic	$ 0.05	$ (1.11)	$ (0.40)
Earnings (loss) per common share – diluted	$ 0.05	$ (1.11)	$ (0.40)
Network Solutions [Member]
Sales
Total Sales	$ 438,015,000	$ 455,226,000	$ 458,232,000
Cost of Sales
Total Cost of Sales	244,226,000	263,677,000	278,929,000
Gross Profit	193,789,000	191,549,000	179,303,000
Services & Support [Member]
Sales
Total Sales	68,495,000	74,835,000	71,045,000
Cost of Sales
Total Cost of Sales	44,733,000	47,217,000	46,783,000
Gross Profit	$ 23,762,000	$ 27,618,000	$ 24,262,000

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net Income (Loss)	$ 2,378	$ (52,982)	$ (19,342)
Other Comprehensive Income (Loss), net of tax
Net unrealized gains (losses) on available-for-sale securities	316	279	(3,130)
Defined benefit plan adjustments	(395)	(1,185)	(3,755)
Foreign currency translation	4,857	(1,480)	(4,236)
Other Comprehensive Income (Loss), net of tax	4,778	(2,386)	(11,121)
Comprehensive Income (Loss), net of tax	$ 7,156	$ (55,368)	$ (30,463)

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member]Cumulative Effect, Period of Adoption, Adjustment [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]Cumulative Effect, Period of Adoption, Adjustment [Member]
Beginning Balance at Dec. 31, 2017	$ 497,911		$ 797	$ 260,515	$ 922,178		$ (682,284)	$ (3,295)
Beginning Balance (ASU 2016-01 [Member]) at Dec. 31, 2017		$ 3,220				$ 3,220
Beginning Balance (ASU 2014-09 [Member]) at Dec. 31, 2017		278				278
Beginning Balance, Shares at Dec. 31, 2017			79,652
Net income (loss)	(19,342)				(19,342)
Other comprehensive income (loss), net of tax	(11,121)							(11,121)
Dividend payments ($0.09 per share)	(17,267)				(17,267)
Dividends accrued on unvested restricted stock units	(7)				(7)
Stock options exercised	1,483				(603)		2,086
PSUs, RSUs and restricted stock vested	(499)				(4,482)		3,983
Purchase of treasury stock	(15,532)						(15,532)
Stock-based compensation expense	7,155			7,155
Ending Balance at Dec. 31, 2018	446,279		$ 797	267,670	883,975		(691,747)	(14,416)
Ending Balance (ASU 2016-02 [Member]) at Dec. 31, 2018		$ 4				4
Ending Balance (ASU 2018-02 [Member]) at Dec. 31, 2018						$ (385)			$ 385
Ending Balance, Shares at Dec. 31, 2018			79,652
Net income (loss)	(52,982)				(52,982)
Other comprehensive income (loss), net of tax	(2,386)							(2,386)
Dividend payments ($0.09 per share)	(17,212)				(17,212)
Dividends accrued on unvested restricted stock units	(10)				(10)
Stock options exercised	526				(208)		734
PSUs, RSUs and restricted stock vested	(571)				(6,480)		5,909
Purchase of treasury stock	(184)						(184)
Stock-based compensation expense	6,962			6,962
Ending Balance at Dec. 31, 2019	380,426		$ 797	274,632	806,702		(685,288)	(16,417)
Ending Balance (ASU 2018-02 [Member]) at Dec. 31, 2019	$ 385
Ending Balance, Shares at Dec. 31, 2019	79,652		79,652
Net income (loss)	$ 2,378				2,378
Other comprehensive income (loss), net of tax	4,778							4,778
Dividend payments ($0.09 per share)	(17,334)				(17,334)
Dividends accrued on unvested restricted stock units	(180)				(180)
Deferred compensation adjustments, net of tax	(2,806)						(2,806)
PSUs, RSUs and restricted stock vested	(1,152)				(9,753)		8,601
Stock-based compensation expense	6,834			6,834
Ending Balance at Dec. 31, 2020	372,944		$ 797	$ 281,466	$ 781,813		$ (679,493)	$ (11,639)
Ending Balance (ASU 2018-02 [Member]) at Dec. 31, 2020	$ 385
Ending Balance, Shares at Dec. 31, 2020	79,652		79,652

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Stockholders Equity [Abstract]
Dividend payments	$ 0.09	$ 0.09	$ 0.09

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net Income (Loss)	$ 2,378,000	$ (52,982,000)	$ (19,342,000)
Adjustments to reconcile net income (loss) to net cash (used in) provided by operating activities:
Depreciation and amortization	16,627,000	17,771,000	15,891,000
Asset impairments	65,000	3,872,000	0
(Gain) loss on investments	(5,802,000)	(11,434,000)	4,050,000
Stock-based compensation expense	6,834,000	6,962,000	7,155,000
Deferred income taxes	(1,356,000)	30,070,000	(17,257,000)
Gain on contingency payment		(1,230,000)
Gain on life insurance proceeds		(1,000,000)
Gain on bargain purchase of a business			(11,322,000)
Other	216,000	(33,000)	17,000
Change in operating assets and liabilities:
Accounts receivable, net	(7,269,000)	8,282,000	49,200,000
Other receivables	(4,732,000)	20,046,000	(8,522,000)
Inventory, net	(25,582,000)	1,252,000	24,192,000
Prepaid expenses and other assets	(5,239,000)	2,749,000	10,727,000
Accounts payable, net	4,543,000	(13,494,000)	(3,799,000)
Accrued expenses and other liabilities	5,093,000	(4,598,000)	(3,226,000)
Income taxes payable	(2,294,000)	(8,705,000)	7,690,000
Net cash provided by (used in) operating activities	(16,518,000)	(2,472,000)	55,454,000
Cash flows from investing activities:
Purchases of property, plant and equipment	(6,413,000)	(9,494,000)	(8,110,000)
Proceeds from disposals of property, plant and equipment	2,000
Proceeds from sales and maturities of available-for-sale investments	105,100,000	47,268,000	153,649,000
Purchases of available-for-sale investments	(56,767,000)	(48,578,000)	(123,209,000)
Acquisition of note receivable	(523,000)
Life insurance proceeds received		1,000,000
Acquisition of business		13,000	(22,045,000)
Net cash provided by (used in) investing activities	41,399,000	(9,791,000)	285,000
Cash flows from financing activities:
Dividend payments	(17,334,000)	(17,212,000)	(17,267,000)
Repayment of bonds payable	(24,600,000)
Tax withholdings related to stock-based compensation settlements	(1,043,000)
Proceeds from stock option exercises		526,000	1,483,000
Purchases of treasury stock		(184,000)	(15,532,000)
Payments on long-term debt		(1,000,000)	(1,100,000)
Net cash used in financing activities	(42,977,000)	(17,870,000)	(32,416,000)
Net increase (decrease) in cash and cash equivalents	(18,096,000)	(30,133,000)	23,323,000
Effect of exchange rate changes	4,502,000	(1,598,000)	(4,252,000)
Cash, cash equivalents and restricted cash, beginning of year	73,773,000	105,504,000	86,433,000
Cash, cash equivalents and restricted cash, end of year	60,179,000	73,773,000	105,504,000
Supplemental disclosure of cash flow information
Cash paid during the year for interest	24,000	512,000	534,000
Cash paid during the year for income taxes	7,609,000	9,357,000	4,104,000
Supplemental disclosure of non-cash investing activities
Purchases of property, plant and equipment included in accounts payable	$ 108,000	$ 90,000	62,000
Contingent payment			$ 1,230,000

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business	Note 1 – Nature of Business ADTRAN, Inc. (“ADTRAN” or the “Company”) is a leading global provider of networking and communications platforms and services focused on the broadband access market. Our vision is to enable a fully connected world where the power to communicate is available to everyone, everywhere. Our unique approach, unmatched industry expertise and innovative solutions enable us to address almost any customer need. Our products and services are utilized by a diverse global customer base of network operators that range from those having regional or national reach and operating as telephone or cable television network operators to alternative network providers such as municipalities or utilities, as well as, managed service providers who serve small- and medium-sized businesses and distributed enterprises. Principles of Consolidation The accompanying Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the U.S. (“U.S. GAAP”) and include the financial position, results of operations, comprehensive income (loss), changes in equity and cash flows of ADTRAN and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. 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, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Our more significant estimates include excess and obsolete inventory reserves, warranty reserves, customer rebates, determination and accrual of the deferred revenue components of multiple element sales agreements, estimated costs to complete obligations associated with deferred revenues and network installations, estimated income tax provision and income tax contingencies, fair value of stock-based compensation, assessment of goodwill and other intangibles for impairment, estimated lives of intangible assets, estimated pension liability, fair value of investments, evaluation of other-than-temporary declines in the value of investments and our allowance for current expected credit losses. Actual amounts could differ significantly from these estimates. We assessed certain accounting matters that generally require consideration of forecasted financial information in context with the information reasonably available to us and the unknown future impacts of the novel coronavirus (“COVID-19”) as of December 31, 2020 and through the date of this report. The accounting matters assessed included, but were not limited to, the allowance for doubtful accounts, current estimated credit losses, stock-based compensation, excess and obsolete inventory reserves, carrying value of goodwill, intangibles and other long-lived assets, financial assets, valuation allowances for tax assets and revenue recognition. While there was not a material impact to our consolidated financial statements as of and for the year ended December 31, 2020 resulting from these assessments, future conditions related to the magnitude and duration of the COVID-19 pandemic, as well as other factors, could result in material impacts to our consolidated financial statements in future reporting periods. Correction of Immaterial Misstatement During the three months ended June 30, 2019, the Company determined that there was an immaterial misstatement of its excess and obsolete inventory reserves in its previously issued annual and interim financial statements. The Company corrected this misstatement by recognizing a $0.8 million out-of-period adjustment during the three months ended June 30, 2019, which increased its excess and obsolete inventory reserve and cost of goods sold for the period. For the six and twelve months ended June 30, 2019 and December 31, 2019, respectively, the out-of-period adjustment was a cumulative $0.2 million reduction in its excess and obsolete inventory reserve and cost of goods sold. Management determined that the correction of this misstatement was not material to any of its previously issued financial statements on both a quantitative and qualitative basis. During the first quarter of 2020, it was determined that certain investments held in the Company’s stock for a deferred compensation plan accounted for as a Rabbi trust were incorrectly classified as long-term investments with the fair value of such investments incorrectly marked to market at each period end rather than classified as treasury stock held at historical cost. This plan has been in existence since 2011. The Company corrected this misstatement as an out-of-period adjustment in the three months ended March 31, 2020 and the twelve months ended December 31, 2020, by remeasuring the investment assets to their historical cost basis through the recording of a net investment gain of $1.5 million in the Consolidated Statement of Income (Loss) and then correcting the classification by decreasing the long-term investment balance at its remeasured cost basis of $2.8 million to treasury stock in the Consolidated 2020 Balance Sheet. Management has determined that this misstatement was not material to any of its previously issued financial statements and that correction of the misstatement was not material to the 2020 annual financial results on either a quantitative or qualitative basis. Summary of Significant Accounting Policies Cash and Cash Equivalents Cash and cash equivalents represent demand deposits, money market funds and short-term investments classified as available-for-sale with original maturities of three months or less. We maintain depository investments with certain financial institutions. As of December 31, 2020, $56.3 million of our cash and cash equivalents, primarily certain domestic money market funds and foreign depository accounts, were in excess of government provided insured depository limits. Although these depository investments may exceed government insured depository limits, we have evaluated the credit worthiness of these applicable financial institutions and determined the risk of material financial loss due to the exposure of such credit risk to be minimal. Restricted Cash Restricted cash consists of certain collateral which secures the Company’s performance obligation under a contract with a certain customer. Financial Instruments The carrying amounts reported in the Consolidated Balance Sheets for cash and cash equivalents, accounts receivable, and accounts payable approximate fair value due to the immediate or short-term maturity of these financial instruments. The carrying amount reported for bonds payable was $24.6 million, which was its fair value as of December 31, 2019. Investments with contractual maturities beyond one year may be classified as short-term based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. Despite the long-term nature of their stated contractual maturities, we routinely buy and sell these securities and we believe we have the ability to quickly sell them to the remarketing agent, tender agent or issuer at par value plus accrued interest in the event we decide to liquidate our investment in a particular variable rate demand note. All income generated from these investments is recorded as interest income. We have not recorded any losses relating to variable rate demand notes. Long-term investments is comprised of deferred compensation plan assets, corporate bonds, municipal fixed-rate bonds, asset-backed bonds, mortgage/agency-backed bonds, U.S. and foreign government bonds, marketable equity securities and other equity investments. Marketable equity securities are reported at fair value as determined by the most recently traded price of the securities at the balance sheet date, although the securities may not be readily marketable due to the size of the available market. Any changes in fair value are recognized in net investment gain (loss). Realized gains and losses on sales of debt securities are computed under the specific identification method and are included in other income (expense). See Note 6 for additional information. Accounts Receivable We record accounts receivable at net realizable value. Prior to establishing payment terms for a new customer, we evaluate the credit risk of the customer. Credit limits and payment terms established for new customers are re-evaluated periodically based on customer collection experience and other financial factors. As of December 31, 2020, single customers comprising more than 10% of our total accounts receivable balance included three customers, which accounted for 41.5% of our total accounts receivable. As of December 31, 2019, single customers comprising more than 10% of our total accounts receivable balance included four customers, which accounted for 53.2% of our total accounts receivable. On January 1, 2020, we adopted ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . Accounting Policy Under Topic 326 We regularly review the need for an allowance for credit losses related to our outstanding accounts receivable balances using the historical loss-rate method as well as assessing asset-specific risks. The assessment of asset-specific risks included the evaluation of relevant available information, from internal and external sources, relating to current conditions that may affect a customer’s ability to pay, such as the customer’s current financial condition or credit rating by geographic location, as provided by a third party and/or by customer, if needed, and overall macro-economic conditions in which the customer operates. Based on this assessment, an allowance for credit loss would be recorded if the Company determined that, based on our historical write-offs, which have been immaterial, and such asset specific risks, there was risk in collectability of the full amount of any accounts receivable. Accounting Policy Prior to Adoption of Topic 326 Prior to adoption of Topic 326 on January 1, 2020, we regularly reviewed the need to maintain an allowance for doubtful accounts and considered factors such as the age of accounts receivable balances, the current economic conditions that may affect a customer’s ability to pay, significant one-time events impacting these customers and our historical experience. If the financial condition of a customer deteriorated, resulting in an impairment of their ability to make payments, we may have been required to record an allowance for doubtful accounts. Inventory Inventory is carried at the lower of cost and estimated net realizable value, with cost being determined using the first-in, first-out method. Standard costs for material, labor and manufacturing overhead are used to value inventory and are updated at least quarterly. We establish reserves for estimated excess and obsolete inventory equal to the difference between the cost of the inventory and the estimated net realizable value of the inventory based on estimated reserve percentages, which consider historical usage, known trends, inventory age and market conditions. When we dispose of excess and obsolete inventories, the related disposals are charged against the inventory reserve. See Note 7 for additional information. Property, Plant and Equipment Property, plant and equipment, which is stated at cost, is depreciated using the straight-line method over the estimated useful lives of the assets. We depreciate building and land improvements from five to 39 years, office machinery and equipment from three to seven years, engineering machinery and equipment from three to seven years, and computer software from three to five years. Expenditures for repairs and maintenance are charged to expense as incurred. Major improvements that materially prolong the lives of the assets are capitalized. Gains and losses on the disposal of property, plant and equipment are recorded in operating income (loss). See Note 8 for additional information. Intangible Assets Purchased intangible assets with finite lives are carried at cost less accumulated amortization. Amortization is recorded over the estimated useful lives of the respective assets, which is two to 14 years . Impairment of Long-Lived Assets and Intangibles Long-lived assets used in operations and intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable and the undiscounted cash flows estimated to be generated by the asset are less than the asset’s carrying value. An impairment loss would be recognized in the amount by which the recorded value of the asset exceeds the fair value of the asset, measured by the quoted market price of an asset or an estimate based on the best information available in the circumstances. During the years ended December 31, 2020 and December 31, 2019, we recognized an impairment loss of less than $0.1 million and $3.9 million, respectively, related to the abandonment of certain information technology implementation projects for which we had previously capitalized expenses. There were no impairment losses for long-lived assets during the year ended December 31, 2018, or for intangible assets recognized during the years ended December 31, 2020, 2019 or 2018. Goodwill Goodwill represents the excess purchase price over the fair value of net assets acquired. We evaluate the carrying value of goodwill during the fourth quarter of each year and between annual evaluations if events occur or circumstances change that would more likely than not reduce the fair value of the reporting unit below its carrying amount. We have elected to by-pass a qualitative assessment to determine whether it is more likely than not that the fair value of the reporting unit to which the goodwill is assigned is less than its carrying amount and, in turn, performed a step-1 analysis of goodwill. No impairment charges related to goodwill were recognized during the years ended December 31, 2020, 2019 and 2018. Liability for Warranty Our products generally include warranties of 90 days to five years for product defects. We accrue for warranty returns at the time of product shipment based on our historical return rate and estimate of the cost to repair or replace the defective products. We engage in extensive product quality programs and processes, including actively monitoring and evaluating the quality of our component suppliers. The increasing complexity of our products will cause warranty incidences, when they arise, to be more costly. Our estimates regarding future warranty obligations may change due to product failure rates, material usage and other rework costs incurred in correcting a product failure. In addition, from time to time, specific warranty accruals may be recorded if unforeseen problems arise. Should our actual experience relative to these factors be worse than our estimates, we will be required to record additional warranty expense. The liability for warranty obligations totaled $7.1 million and $8.4 million as of December 31, 2020 and 2019, respectively. These liabilities are included in accrued expenses and other liabilities in the accompanying Consolidated Balance Sheets. A summary of warranty expense and write-off activity for the years ended December 31, 2020, 2019 and 2018 is as follows: Year Ended December 31, (In thousands) 2020 2019 2018 Balance at beginning of period $ 8,394 $ 8,623 $ 9,724 Plus: Amounts charged to cost and expenses 1,538 4,569 7,392 Less: Deductions (2,786 ) (4,798 ) (8,493 ) Balance at end of period $ 7,146 $ 8,394 $ 8,623 Pension Benefit Plan Obligations We maintain a defined benefit pension plan covering employees in certain foreign countries. Pension benefit plan obligations are based on various assumptions used by our actuaries in calculating these amounts. These assumptions include discount rates, compensation rate increases, expected return on plan assets, retirement rates and mortality rates. Actual results that differ from the assumptions and changes in assumptions could affect future expenses and obligations. Our net pension liability totaled $18.7 million and $15.9 million as of December 31, 2020 and 2019, respectively. Stock-Based Compensation We have two stock incentive plans from which stock options, performance stock units (“PSUs”), restricted stock units (“RSUs”) and restricted stock are available for grant to employees and directors. Costs related to these awards are recognized over their vesting periods. All employee and director stock options granted under our stock option plans have an exercise price equal to the fair market value of the award, as defined in the plan, of the underlying common stock on the grant date. All of our outstanding stock option awards are classified as equity awards and therefore are measured at fair value on their grant date. Stock-based compensation expense recognized for the years ended December 31, 2020, 2019 and 2018 was approximately $6.8 million, $7.0 million and $7.2 million, respectively. As of December 31, 2020, total unrecognized compensation cost related to non-vested stock options, PSUs, RSUs and restricted stock was approximately $16.7 million, which is expected to be recognized over an average remaining recognition period of 2.9 years. See Note 5 for additional information. Research and Development Costs Research and development costs include compensation for engineers and support personnel, contracted services, depreciation and material costs associated with new product development, enhancement of current products and product cost reductions. We continually evaluate new product opportunities and engage in intensive research and product development efforts. Research and development costs totaled $113.3 million, $126.2 million and $124.5 million for the years ended December 31, 2020, 2019 and 2018, respectively. Other Comprehensive Income (Loss) The following table presents changes in accumulated other comprehensive income (loss), net of tax, by components of accumulated other comprehensive income (loss) for the years ended December 31, 2020 2019 and 2018: (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption (2) Total Balance as of December 31, 2017 $ 2,567 $ (4,286 ) $ (1,576 ) $ — $ (3,295 ) Other comprehensive loss before reclassifications 685 (3,890 ) (4,236 ) — (7,441 ) Amounts reclassified to retained earnings (1) (3,220 ) — — — (3,220 ) Amounts reclassified from accumulated other comprehensive loss (595 ) 135 — — (460 ) Balance as of December 31, 2018 (563 ) (8,041 ) (5,812 ) — (14,416 ) Other comprehensive loss before reclassifications 573 (1,717 ) (1,480 ) — (2,624 ) Amounts reclassified to retained earnings (1) — — — 385 385 Amounts reclassified from accumulated other comprehensive loss (294 ) 532 — — 238 Balance as of December 31, 2019 (284 ) (9,226 ) (7,292 ) 385 (16,417 ) Other comprehensive loss before reclassifications 749 (1,231 ) 4,857 — 4,375 Amounts reclassified from accumulated other comprehensive loss (433 ) 836 — — 403 Balance as of December 31, 2020 $ 32 $ (9,621 ) $ (2,435 ) $ 385 $ (11,639 ) (1) With the adoption of ASU 2016-01, the unrealized gains on our equity investments were reclassified to retained earnings. (2) With the adoption of ASU 2018-02 on January 1, 2019, stranded tax effects related to the Tax Cuts and Jobs Act of 2017 were reclassified to retained earnings. See Note 14 for additional information. The following tables present the details of reclassifications out of accumulated other comprehensive income (loss) for the years ended December 31, 2020, 2019 and 2018: (In thousands) For the year ended December 31, Details about Accumulated Other Comprehensive Income Components 2020 2019 2018 Affected Line Item in the Statement Where Net Income Is Presented Unrealized gains on available-for-sale securities: Net realized gain on sales of securities $ 585 $ 397 $ 804 Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (1,212 ) (771 ) (196 ) (1) Total reclassifications for the period, before tax (627 ) (374 ) 608 Tax benefit 224 136 (148 ) Total reclassifications for the period, net of tax $ (403 ) $ (238 ) $ 460 (1) Included in the computation of net periodic pension cost. See Note 15 for additional information. The following tables present the tax effects related to the change in each component of other comprehensive income (loss) for the years ended December 31, 2020, 2019 and 2018: 2020 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gains (losses) on available-for-sale securities $ 1,012 $ (263 ) $ 749 Reclassification adjustment for amounts related to available-for-sale investments included in net income (585 ) 152 (433 ) Defined benefit plan adjustments (1,784 ) 553 (1,231 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income 1,212 (376 ) 836 Foreign currency translation adjustment 4,857 — 4,857 Total Other Comprehensive Income (Loss) $ 4,712 $ 66 $ 4,778 2019 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gains (losses) on available-for-sale securities $ 774 $ (201 ) $ 573 Reclassification adjustment for amounts related to available-for-sale investments included in net loss (397 ) 103 (294 ) Defined benefit plan adjustments (2,488 ) 771 (1,717 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net loss 771 (239 ) 532 Foreign currency translation adjustment (1,480 ) — (1,480 ) Total Other Comprehensive Income (Loss) $ (2,820 ) $ 434 $ (2,386 ) 2018 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gains (losses) on available-for-sale securities $ 926 $ (241 ) $ 685 Reclassification adjustment for amounts related to available-for-sale investments included in net loss (804 ) 209 (595 ) Reclassification adjustment for amounts reclassed to retained earnings related to the adoption of ASU 2016-01 (4,351 ) 1,131 (3,220 ) Defined benefit plan adjustments (5,638 ) 1,748 (3,890 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net loss 196 (61 ) 135 Foreign currency translation adjustment (4,236 ) — (4,236 ) Total Other Comprehensive Income (Loss) $ (13,907 ) $ 2,786 $ (11,121 ) Income Taxes The provision for income taxes has been determined using the asset and liability approach of accounting for income taxes. Under this approach, deferred taxes represent the future tax consequences expected to occur when the reported amounts of assets and liabilities are recovered or paid. The provision for income taxes represents income taxes paid or payable for the current year plus the change in deferred taxes during the year. Deferred taxes result from the difference between financial and tax bases of our assets and liabilities and are adjusted for changes in tax rates and tax laws when such changes are enacted. Valuation allowances are recorded to reduce deferred tax assets when it is more likely than not that a tax benefit will not be realized. We establish reserves to remove some or all of the tax benefit of any of our tax positions at the time we determine that the positions become uncertain. We adjust these reserves, including any impact on the related interest and penalties, as facts and circumstances change. Foreign Currency Transactions with customers that are denominated in foreign currencies are recorded using the appropriate exchange rates from throughout the year. Assets and liabilities denominated in foreign currencies are remeasured at the balance sheet dates using the closing rates of exchange between those foreign currencies and the functional currency with any transaction gains or losses reported in other income (expense). Our primary exposures to foreign currency exchange rate movements are with our German subsidiary, whose functional currency is the Euro, our Australian subsidiary, whose functional currency is the Australian dollar and our British subsidiary, whose functional currency is the Great British pound. Adjustments resulting from translating financial statements of international subsidiaries are recorded as a component of accumulated other comprehensive income (loss). Revenue On January 1, 2018, we adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606), Revenue Recognition. Accounting Policy under Topic 606 Revenue is measured based on the consideration expected to be received in exchange for transferring goods or providing services to a customer and as performance obligations under the terms of the contract are satisfied. Generally, this occurs with the transfer of control of a product to the customer. Review of contracts with customers, for both direct customers and distributors, are performed and assessment made regarding principal versus agent considerations to determine primary responsibility for delivery of performance obligation, presumed inventory risk, and discretion in establishing pricing, when applicable. For transactions where there are multiple performance obligations, individual products and services are accounted for separately if they are distinct (if a product or service is separately identifiable from other items and if a customer can benefit from it on its own or with other resources that are readily available to the customer). The consideration, including any discounts, is allocated between separate products and services based on their stand-alone selling prices. Stand-alone selling prices are determined based on the prices at which the separate products and services are sold and are allocated based on each item’s relative value to the total value of the products and services in the arrangement. For items that are not sold separately, we estimate stand-alone selling prices primarily using the “expected cost plus a margin” approach. Payment terms are generally 30 days in the U.S. and typically longer in many geographic markets outside the U.S. Revenue is generated by two reportable segments: Network Solutions and Services & Support. Network Solutions Segment - Includes hardware products and software defined next-generation virtualized solutions used in service provider or business networks, as well as prior generation products. The majority of the revenue from this segment is from hardware revenue. Hardware and Software Revenue Revenue from hardware sales is recognized when control is transferred to the customer, which is generally when the products are shipped. Shipping terms are generally FOB shipping point. Revenue from software license sales are recognized at delivery and transfer of control to the customer. Revenue is recorded net of estimated discounts and rebates using historical trends. Customers are typically invoiced when control is transferred and revenue is recognized. Our products generally include assurance-based warranties of 90 days to five years for product defects, which are accrued at the time products are delivered. Services & Support Segment - A complete portfolio of maintenance, network implementation and solutions integration and managed services, which include hosted cloud services and subscription services to complement our Network Solutions segment. Maintenance Revenue Our maintenance service periods range from one month to five years. Customers are typically invoiced and pay for maintenance services at the beginning of the maintenance period. We recognize revenue for maintenance services on a straight-line basis over the maintenance period as our customers benefit evenly throughout the contract term and deferred revenues, when applicable, are recorded in current and non-current unearned revenue. Network Implementation Revenue We recognize revenue for network implementation, which primarily consists of engineering, execution and enablement services at a point in time when each performance obligation is complete. If we have recognized revenue but have not billed the customer, the right to consideration is recognized as a contract asset that is included in other receivables on the Consolidated Balance Sheet. The contract asset is transferred to accounts receivable when the completed performance obligation is invoiced to the customer. See Notes 4 and 16 for additional information on reportable segments. Unearned Revenue Unearned revenue primarily represents customer billings on maintenance service programs and unearned revenues related to multiple element contracts where we still have contractual obligations to our customers. We currently offer maintenance contracts ranging from one month to five years. Revenue attributable to maintenance contracts is recognized on a straight-line basis over the related contract term. In addition, we provide software maintenance and a variety of hardware maintenance services to customers under contracts with terms up to ten years. When we defer revenue related to multiple performance obligations where we still have contractual obligations, we also defer the related costs. Current deferred costs are included in prepaid expenses and other current assets on the accompanying Consolidated Balance Sheets and totaled $1.1 million and $1.6 million as of December 31, 2020 and 2019, respectively. Non-current deferred costs are included in other non-current assets on the accompanying Consolidated Balance Sheets and totaled less than $0.1 million and $0.1 million as of December 31, 2020 and 2019, respectively. Earnings (Loss) per Share Earnings (loss) per common share and earnings (loss) per common share assuming dilution, are based on the weighted average number of common shares and, when dilutive, common equivalent shares outstanding during the year. See Note 19 for additional information. Business Combinations The Company records assets acquired, liabilities assumed, contractual contingencies, when applicable, and intangible assets recognized as part of business combinations based on their fair values on the date of acquisition. The excess of the purchase price over the estimated fair values of the net tangible and intangible assets and liabilities assumed or acquired is recorded as goodwill. If the estimated fair values of net tangible and intangible assets acquired and liabilities assumed exceed the purchase price, a bargain purchase gain is recorded. The Company’s estimates of fair value are based on historical experience, industry knowledge, certain information obtained from the management of the acquired company and, in some cases, valuations performed by independent third-party firms. The results of operations of acquired companies are included in the accompanying Consolidated Statements of Income (Loss) since their dates of acquisition. Costs incurred to complete the business combination, such as legal, accounting or other professional fees are charged to selling, general and administrative expenses as incurred. Recently Adopted Accounting Pronouncements In August 2018, the Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2 Compensation – Retirement Benefits – Defined Benefit Plans – General (Subtopic 715-20): Disclosure Framework – Changes to the Disclosure Requirements for Defined Benefit Plans, In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, Fair Value Measurement. Concepts Statement No. 8 — Conceptual Framework for Financial Reporting — Chapter 8 — Notes to Financial Statements In August 2018, the FASB issued ASU 2018-15, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement. The following table illustrates the impact of adoption of ASU 2018-15 on the Consolidated Balance Sheet as of December 31, 2019: As of December 31, 2019 (In thousands) Pre-Adoption Effect of Adoption As Presented Now Consolidated Balance Sheet Property, plant and equipment, net $ 73,708 $ (5,622 ) $ 68,086 Other non-current assets $ 14,261 $ 5,622 $ 19,883 There was no impact upon adoption of ASU 2018-15 on the Consolidated Statement of Income (Loss) fo

Cash, Cash Equivalents and Rest

Cash, Cash Equivalents and Restricted Cash	12 Months Ended
	Dec. 31, 2020
Cash And Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash	Note 2 – Cash, Cash Equivalents and Restricted Cash The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Consolidated Balance Sheet that sum to the total of the same such amounts shown in the Consolidated Statement of Cash Flows: (In thousands) December 31, 2020 Cash and cash equivalents $ 60,161 Restricted cash 18 Cash, cash equivalents and restricted cash $ 60,179 The Company did not have any restricted cash as of December 31, 2019 and 2018. See Note 17 for additional information regarding restricted cash.

Business Combinations

Business Combinations	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
Business Combinations	Note 3 – Business Combinations In November 2018, we acquired SmartRG, Inc., for cash consideration. This transaction was accounted for as a business combination. We recorded goodwill of $3.5 million as a result of this acquisition, which represents the excess of the purchase price over the fair value of net assets acquired and liabilities assumed. The financial results of this acquisition are included in the consolidated financial statements since the date of acquisition. The revenues are included in the Subscriber Solutions & Experience category within the Network Solutions and Services & Support reportable segments. Contingent liabilities with a fair value totaling $1.2 million were recognized at the acquisition date. The required milestones were not achieved and therefore, a gain of $1.2 million was recognized upon the reversal of these liabilities during the second quarter of 2019. An escrow in the amount of $2.8 million was set up at the acquisition date to fund post-closing working capital settlements and to satisfy indemnity obligations to the Company arising from any inaccuracy or breach of representations, warranties, covenants, agreements or obligations of the sellers. The escrow was subject to arbitration. In December 2019, $1.3 million of the $2.8 million was released from the escrow account pursuant to the agreement and the remaining balance was released in December 2020. In March 2018 The Consolidated Statement of Income for the year ended December 31, 2018 includes the following revenue and net loss attributable to SmartRG and Sumitomo since the date of acquisition: (In thousands) March 19, 2018 to December 31, 2018 Revenue $ 9,186 Net loss $ (1,297 ) The following unaudited supplemental pro forma information presents the financial results as if the acquisition of SmartRG and Sumitomo had occurred on January 1, 2017. This unaudited supplemental pro forma information does not purport to be indicative of what would have occurred had the acquisition been completed on January 1, 2018, nor is it indicative of any future results. There were no material, non-recurring adjustments to this unaudited pro forma information. (In thousands) 2018 Pro forma revenue $ 559,050 Pro forma net loss $ (33,862 ) For the years ended December 31, 2020, 2019 and 2018, we incurred acquisition and integration related expenses and amortization of acquired intangibles of $3.8 million, $5.0 million and $2.9 million, respectively, related to the SmartRG and Sumitomo acquisitions.

Revenue

Revenue	12 Months Ended
	Dec. 31, 2020
Revenue From Contract With Customer [Abstract]
Revenue	Note 4 - Revenue The following is a description of the principal activities from which revenue is generated by reportable segment: Network Solutions - Includes hardware products and software-defined next-generation virtualized solutions used in service provider or business networks, as well as prior generation products. Services & Support - Includes maintenance, network implementation, solutions integration and managed services, which include hosted cloud services and subscription services. Revenue by Category In addition to reportable segments, revenue is also reported for the following three categories – Access & Aggregation, Subscriber Solutions & Experience and Traditional & Other Products. The following table disaggregates revenue by reportable segment and revenue category for the year ended December 31, 2020: (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 262,578 $ 50,560 $ 313,138 Subscriber Solutions & Experience 161,824 9,263 171,087 Traditional & Other Products 13,613 8,672 22,285 Total $ 438,015 $ 68,495 $ 506,510 The following table disaggregates revenue by reportable segment and revenue category for the year ended December 31, 2019: (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 289,980 $ 58,894 $ 348,874 Subscriber Solutions & Experience 144,651 8,269 152,920 Traditional & Other Products 20,595 7,672 28,267 Total $ 455,226 $ 74,835 $ 530,061 The following table disaggregates revenue by reportable segment and revenue category for the year ended December 31, 2018: (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 301,801 $ 57,069 $ 358,870 Subscriber Solutions & Experience 129,067 5,393 134,460 Traditional & Other Products 27,364 8,583 35,947 Total $ 458,232 $ 71,045 $ 529,277 Revenue allocated to remaining performance obligations represents contract revenues that have not yet been recognized for contracts with a duration greater than one year. As of December 31, 2020, we did not have any significant performance obligations related to customer contracts that had an original expected duration of one year or more, other than maintenance services, which are satisfied over time. As a practical expedient, for certain contracts we recognize revenue equal to the amounts we are entitled to invoice, which correspond to the value of completed performance obligations to date. The amount related to these performance obligations was $17.7 million and $13.6 million as of December 31, 2020 and December 31, 2019, respectively. The Company expects to recognize 61% of the $17.7 million as of December 31, 2020 over the next 12 months, with the remainder to be recognized thereafter. The following table provides information about accounts receivable, contract assets and unearned revenue from contracts with customers: (In thousands) December 31, 2020 December 31, 2019 Accounts receivable $ 98,827 $ 90,531 Contract assets (1) $ 63 $ 2,812 Unearned revenue $ 14,092 $ 11,963 Non-current unearned revenue $ 6,888 $ 6,012 (1) Of the outstanding unearned revenue balance as of December 31, 2019 and December 31, 2018, $11.0 million and $12.7 million were recognized as revenue during the years ended December 31, 2020 and 2019, respectively.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	Note 5 – Stock-Based Compensation The following table summarizes stock-based compensation expense related to stock options, PSUs, RSUs and restricted stock for the years ended December 31, 2020, 2019 and 2018: (In thousands) 2020 2019 2018 Stock-based compensation expense included in cost of sales $ 426 $ 369 $ 418 Selling, general and administrative expenses 4,036 3,889 3,989 Research and development expenses 2,372 2,704 2,748 Stock-based compensation expense included in operating expenses 6,408 6,593 6,737 Total stock-based compensation expense 6,834 6,962 7,155 Tax benefit for expense associated with non-qualified stock options, PSUs, RSUs and restricted stock (1,629 ) (1,659 ) (1,432 ) Total stock-based compensation expense, net of tax $ 5,205 $ 5,303 $ 5,723 Stock Incentive Program Descriptions 2020 Stock Incentive Plans At the annual meeting of stockholders held on May 13, 2020, the Company’s stockholders approved, upon recommendation of the Board of Directors, the adoption of the ADTRAN, Inc. 2020 Employee Stock Incentive Plan (the “2020 Employee Plan”) as well as the ADTRAN, Inc. 2020 Directors Stock Plan (the “2020 Directors Plan”). No additional awards will be granted under the Company’s previous stock incentive plans, the ADTRAN, Inc. 2015 Employee Stock Incentive Plan (the “2015 Employee Plan”) or the 2010 Directors Stock Plan (the “2010 Directors Plan”) subsequent to the stockholders’ approval of these new stock plans. Outstanding awards granted under the 2015 Employee Plan and the 2010 Directors Plan will remain subject to the terms of such plans, and shares underlying awards granted under such plans that are cancelled or forfeited will be available for issuance under the 2020 Employee Plan or the 2020 Directors Plan, as applicable. Under the 2020 Employee Plan, the Company is authorized to issue 2.8 million shares of common stock to certain employees, key service providers and advisors through incentive stock options and non-qualified stock options, stock appreciation rights, RSUs and restricted stock, any of which may be subject to performance-based conditions. RSUs and restricted stock granted under the 2020 Employee Plan will typically vest pursuant to a four-year four-year ten-year Under the 2020 Directors Plan, the Company is authorized to issue 0.4 million shares of common stock through stock options, restricted stock and RSUs to non-employee directors. Stock awards issued under the 2020 Directors Plan typically will become vested in full on the first anniversary of the grant date. Stock options issued under the 2020 Directors Plan will have a ten-year Previous Stock Incentive Plans In January 2015, the Board of Directors adopted the 2015 Employee Plan, which authorized 7.7 million shares of common stock for issuance to certain employees and officers through incentive stock options and non-qualified stock options, stock appreciation rights, PSUs, RSUs and restricted stock. The 2015 Employee Plan was adopted by stockholder approval at our annual meeting of stockholders held in May 2015. PSUs, RSUs and restricted stock granted under the 2015 Plan reduce the shares authorized for issuance under the 2015 Employee Plan by 2.5 shares of common stock for each share underlying the award. Options granted under the 2015 Employee Plan typically become exercisable beginning after one year of continued employment, normally pursuant to a four-year ten-year In January 2006, the Board of Directors adopted the ADTRAN, Inc. 2006 Employee Stock Incentive Plan (the “2006 Plan”), which authorized 13.0 million shares of common stock for issuance to certain employees and officers through incentive stock options and non-qualified stock options, stock appreciation rights, RSUs and restricted stock. Options granted under the 2006 Plan typically become exercisable beginning after one year of continued employment, normally pursuant to a four-year ten-year In May 2010, the Company’s stockholders approved the 2010 Directors Plan, under which 0.5 million shares of common stock have been reserved for issuance. This plan replaced the 2005 Directors Stock Option Plan. Under the 2010 Directors Plan, the Company may issue stock options, restricted stock and RSUs to our non-employee directors. Stock awards issued under the 2010 Directors Plan become vested in full on the first anniversary of the grant date. Options issued under the 2010 Directors Plan had a ten-year PSUs, RSUs and restricted stock The following table is a summary of our PSUs, RSUs and restricted stock outstanding as of December 31, 2019 and 2020 and the changes that occurred during 2020: Number of shares ( In thousands Weighted Average Grant Date Fair Value Unvested PSUs, RSUs and restricted stock outstanding, December 31, 2019 1,891 $ 14.58 PSUs, RSUs and restricted stock granted 1,029 $ 11.02 PSUs, RSUs and restricted stock vested (453 ) $ 14.26 PSUs, RSUs and restricted stock forfeited (621 ) $ 18.14 Unvested PSUs, RSUs and restricted stock outstanding, December 31, 2020 1,846 $ 11.49 The following table details the significant assumptions that impact the fair value estimate of the market-based PSUs: 2020 2019 2018 Estimated fair value per share $14.43 $9.53 to $18.05 $16.59 Expected volatility 51.88% 32.7% to 38.9% 27.98% to 31.58% Risk-free interest rate 0.24% 1.6% to 2.46% 2.11% to 2.99% Expected dividend yield 2.85% 2.3% to 4.09% 1.83% to 2.49% For market-based PSUs, the number of shares of common stock earned by a recipient is subject to a market condition based on ADTRAN’s relative total shareholder return against all companies in the NASDAQ Telecommunications Index at the end of a three-year During the first quarter of 2020, the Company issued 0.3 million performance-based PSUs under the 2015 Employee Plan to its executive officers. The grant-date fair value of these performance-based awards is based on the closing price of the Company’s stock on the date of grant. Subject to the grantee’s continued employment, the grantee has the ability to earn shares in a range of 0% to 142.8% of the awarded number of PSUs based on the achievement of a defined performance target at the end of a three-year The fair value of RSUs and restricted stock is equal to the closing price of our stock on the grant date. RSUs and restricted stock vest ratably over four-year one-year We will continue to assess the assumptions and methodologies used to calculate the estimated fair value of stock-based compensation. If circumstances change, and additional data becomes available over time, we may change our assumptions and methodologies, which may materially impact our fair value determination. As of December 31, 2020, total unrecognized compensation expense related to the non-vested portion of market-based PSUs, RSUs and restricted stock was approximately $16.7 million, which is expected to be recognized over an average remaining recognition period of 2.9 years and will be adjusted for actual forfeitures as they occur. As of December 31, 2020, 3.6 million shares were available for issuance under shareholder-approved equity plans in connection with the grant and exercise of stock options, PSU’s, RSU’s or restricted stock. Stock Options The following table is a summary of stock options outstanding as of December 31, 2020 and 2019 and the changes that occurred during 2020: Number of Options ( I Weighted Average Exercise Price (Per share) Weighted Avg. Remaining Contractual Life in Years Aggregate Intrinsic (In thousands) Stock options outstanding, December 31, 2019 3,572 $ 22.88 3.40 $ — Stock options granted — $ — Stock options exercised — $ — Stock options forfeited — $ — Stock options expired (854 ) $ 28.00 Stock options outstanding, December 31, 2020 2,718 $ 21.17 2.86 $ — Stock options exercisable, December 31, 2020 2,718 $ 21.17 2.86 $ — All of these stock options were issued at exercise prices that approximated fair market value at the date of grant. As of December 31, 2020, there was no unrecognized compensation expense related to non-vested stock options. The aggregate intrinsic values represent the total pre-tax intrinsic value (the difference between ADTRAN’s closing stock price on the last trading day of 2020 and the exercise price, multiplied by the number of in-the-money options) that would have been received by the option holders had all option holders exercised their options on December 31, 2020. The amount of aggregate intrinsic value will change based on the fair market value of ADTRAN’s stock and was $0 as of December 31, 2020. The total pre-tax intrinsic value of options exercised during 2020, 2019 and 2018 was $0, $0.1 million and $0.2 million, respectively. The fair value of options fully vesting during 2020, 2019 and 2018 was less than $0.1 million, $0.9 million and $2.5 million, respectively. The following table further describes our stock options outstanding as of December 31, 2020: Options Outstanding Options Exercisable Range of Exercise Prices Options Outstanding at December 31, 2020 (In thousands) Weighted Avg. Remaining Contractual Life in Years Weighted Average Exercise Price Options Exercisable at December 31, 2020 (In thousands) Weighted Average Exercise Price $15.33 – $18.96 1,007 3.69 $ 15.91 1,007 $ 15.91 $18.97 – $23.45 588 3.68 $ 18.97 588 $ 18.97 $23.46 – $30.35 603 2.55 $ 24.11 603 $ 24.11 $30.36 – $41.92 520 0.64 $ 30.40 520 $ 30.40 2,718 2,718 The Black-Scholes option pricing model (the “Black-Scholes Model”) is used to determine the estimated fair value of stock option awards on the date of grant. The Black-Scholes Model requires the input of certain assumptions that involve judgment. Because our stock options have characteristics significantly different from those of traded options, and because changes in the input assumptions can materially affect the fair value estimate, existing models may not provide reliable measures of fair value of our stock options. The stock option pricing model requires the use of several assumptions that impact the fair value estimate. These variables include, but are not limited to, the volatility of our stock price and employee exercise behaviors. There were no stock options granted in during the years ended December 31, 2020, 2019 or 2018.

Investments

Investments	12 Months Ended
	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Investments	Note 6 – Investments Debt Securities and Other Investments As of December 31, 2020, the following debt securities and other investments were included in short-term investments and long-term investments on the Consolidated Balance Sheet and recorded at fair value: Amortized Gross Unrealized Fair (In thousands) Cost Gains Losses Value Corporate bonds $ 11,762 $ 123 $ — $ 11,885 Municipal fixed-rate bonds 2,854 30 — 2,884 Asset-backed bonds 6,634 74 — 6,708 Mortgage/Agency-backed bonds 11,536 114 (6 ) 11,644 U.S. government bonds 9,763 112 — 9,875 Foreign government bonds 1,334 4 (1 ) 1,337 Commercial Paper 250 — — 250 Other 533 — — 533 Available-for-sale debt securities held at fair value $ 44,666 $ 457 $ (7 ) $ 45,116 As of December 31, 2019, the following debt securities and other investments were included in short-term investments and long-term investments on the Consolidated Balance Sheet and recorded at fair value: Amortized Gross Unrealized Fair (In thousands) Cost Gains Losses Value Corporate bonds $ 9,304 $ 80 $ — $ 9,384 Municipal fixed-rate bonds 930 — — 930 Asset-backed bonds 6,867 26 (3 ) 6,890 Mortgage/Agency-backed bonds 6,944 26 (8 ) 6,962 U.S. government bonds 12,311 21 (9 ) 12,323 Foreign government bonds 372 — (1 ) 371 Variable rate demand notes 800 — — 800 Available-for-sale debt securities held at fair value $ 37,528 $ 153 $ (21 ) $ 37,660 As of December 31, 2020, our debt securities had the following contractual maturities: (In thousands) Corporate bonds Municipal fixed-rate bonds Asset-backed bonds Mortgage / Agency-backed bonds U.S. government bonds Foreign government bonds Commercial paper Other Less than one year $ 1,477 $ 96 $ 144 $ 63 $ — $ 75 $ 250 $ 533 One to two years 2,007 1,245 300 2,129 5,122 462 — — Two to three years 7,013 1,246 622 2,940 4,526 498 — — Three to five years 1,388 297 3,658 183 227 302 — — Five to ten years — — 1,241 2,095 — — — — More than ten years — — 743 4,234 — — — — Total $ 11,885 $ 2,884 $ 6,708 $ 11,644 $ 9,875 $ 1,337 $ 250 $ 533 Actual maturities may differ from contractual maturities as some borrowers have the right to call or prepay obligations with or without call or prepayment penalties. Realized gains and losses on sales of securities are computed under the specific identification method. The following table presents gross realized gains and losses related to our debt securities for the years ended December 31, 2020, 2019 and 2018: For the year ended December 31, (In thousands) 2020 2019 2018 Gross realized gains on debt securities $ 459 $ 108 $ 57 Gross realized losses on debt securities (58 ) (50 ) (592 ) Total gain (loss) recognized, net $ 401 $ 58 $ (535 ) The Company’s investment policy provides limitations for issuer concentration, which limits, at the time of purchase, the concentration in any one issuer to 5% of the market value of the total investment portfolio. The Company did not purchase any available-for-sale debt with credit deterioration during the years ended December 31, 2020, 2019 and 2018. The following table presents the breakdown of debt securities and other investments with unrealized losses as of December 31, 2020: Continuous Unrealized Loss Position for Less than 12 Months Continuous Unrealized Loss Position for 12 Months or Greater Total (In thousands) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate bonds $ 336 $ — $ — $ — $ 336 $ — Municipal fixed-rate bonds 310 — — — 310 — Asset-backed bonds 2 — — — 2 — Mortgage/Agency-backed bonds 2,078 (6 ) — — 2,078 (6 ) U.S. government bonds 350 — — — 350 — Foreign government bonds 302 (1 ) — — 302 (1 ) Total $ 3,378 $ (7 ) $ — $ — $ 3,378 $ (7 ) The following table presents the breakdown of debt securities and other investments with unrealized losses as of December 31, 2019: Continuous Unrealized Loss Position for Less than 12 Months Continuous Unrealized Loss Position for 12 Months or Greater Total (In thousands) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate bonds $ 203 $ — $ — $ — $ 203 $ — Municipal fixed-rate bonds 930 — — — 930 — Asset-backed bonds 797 (3 ) — — 797 (3 ) Mortgage/Agency-backed bonds 2,594 (6 ) 136 (2 ) 2,730 (8 ) U.S. government bonds 4,070 (9 ) — — 4,070 (9 ) Foreign government bonds 371 (1 ) — — 371 (1 ) Total $ 8,965 $ (19 ) $ 136 $ (2 ) $ 9,101 $ (21 ) The decrease in unrealized losses during 2020 resulted from changes in market positions associated with our fixed income portfolio. Marketable Equity Securities Marketable equity securities consist of publicly traded stock, funds and certain other investments measured at fair value or cost, where appropriate. During the three months ended March 31, 2019, an outstanding note receivable of $4.3 million was repaid and reissued in the form of debt and equity. Of the outstanding $4.3 million, $3.4 million was issued as an equity investment, which represented a non-cash investing activity. This equity investment, which does not have a readily determinable fair value, was recorded using the measurement alternative. Under the measurement alternative, equity investments that do not have a readily determinable fair value can be recorded at cost less impairment, if any, adjusted for observable price changes for an identical or similar investment. The carrying value of this investment under the measurement alternative was $3.4 million as of December 31, 2019. During the year ended December 31, 2020, impairment charges totaling $2.6 million were recorded related to this equity investment and are included in net investment gain (loss) on the Consolidated Statement of Income (Loss). As a result, the carrying value of this investment was $0.8 million as of December 31, 2020. The remaining amount, $0.9 million of the original $4.3 million note receivable, was reissued as a new note receivable, which is included in long-term investments on the Consolidated Balance Sheets as of December 31, 2020 and December 31, 2019, and represented a non-cash investing activity during the year ended December 31, 2019. No impairment charge was recognized related to the note receivable as it is a secured loan. Realized and unrealized gains and losses for our marketable equity securities for the year ended December 31, 2020, 2019 and 2018 were as follows: For the year ended December 31, (In thousands) 2020 2019 2018 Realized losses on equity securities sold $ (2,382 ) $ (96 ) $ 1,306 Unrealized gains on equity securities held 6,831 11,472 (4,821 ) Total gain (loss) recognized, net $ 4,449 $ 11,376 $ (3,515 ) As of December 31, 2020 and 2019, gross unrealized losses related to individual investments in a continuous loss position for twelve months or longer were not material. U.S. GAAP establishes a three-level valuation hierarchy based upon observable and unobservable inputs for fair value measurement of financial instruments: • Level 1 – Observable outputs; values based on unadjusted quoted prices for identical assets or liabilities in an active market; • Level 2 – Significant inputs that are observable; values based on quoted prices in markets that are not active or model inputs that are observable either directly or indirectly; • Level 3 – Significant unobservable inputs; values based on prices or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement; inputs could include information supplied by investees. The Company’s cash equivalents and investments held at fair value are categorized into this hierarchy as follows: Fair Value Measurements as of December 31, 2020 Using (In thousands) Fair Value Quoted Prices in Active Market for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash equivalents Money market funds $ 497 $ 497 $ — $ — U.S. government bonds 350 350 — — Available-for-sale debt securities Corporate bonds 11,885 — 11,885 — Municipal fixed-rate bonds 2,884 — 2,884 — Asset-backed bonds 6,708 — 6,708 — Mortgage/Agency-backed bonds 11,644 — 11,644 — U.S. government bonds 9,875 9,875 — — Foreign government bonds 1,337 — 1,337 — Commercial paper 250 — 250 — Other investments 533 — — 533 Marketable equity securities Marketable equity securities – various industries 10,963 10,963 — — Deferred compensation plan assets 23,891 23,891 — — Other investments 1,400 1,400 — — Total $ 82,217 $ 46,976 $ 34,708 $ 533 Fair Value Measurements as of December 31, 2019 Using (In thousands) Fair Value Quoted Prices in Active Market for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash equivalents Money market funds $ 1,309 $ 1,309 $ — $ — Available-for-sale debt securities Corporate bonds 9,384 — 9,384 — Municipal fixed-rate bonds 930 — 930 — Asset-backed bonds 6,890 — 6,890 — Mortgage/Agency-backed bonds 6,962 — 6,962 — U.S. government bonds 12,323 12,323 — — Foreign government bonds 371 — 371 — Variable rate demand notes 800 — 800 — Marketable equity securities Marketable equity securities – various industries 35,501 35,501 — — Equity in escrow 298 298 — — Deferred compensation plan assets 21,698 21,698 — — Other investments 2,442 2,442 — — Total $ 98,908 $ 73,571 $ 25,337 $ — The fair value of our Level 2 securities is calculated using a weighted average market price for each security. Market prices are obtained from a variety of industry standard data providers, large financial institutions and other third-party sources. These multiple market prices are used as inputs into a distribution-curve-based algorithm to determine the daily market value of each security. The fair value of Level 3 securities is calculated based on unobservable inputs. Quantitative information with respect to unobservable inputs consisted of third-party valuations performed in accordance with ASC 820 – Fair Value Measurement. Our variable rate demand notes have a structure that implies a standard expected market price. The frequent interest rate resets make it reasonable to expect the price to stay at par. These securities are priced at the expected market price.

Inventory

Inventory	12 Months Ended
	Dec. 31, 2020
Inventory Disclosure [Abstract]
Inventory	Note 7 – Inventory As of December 31, 2020 and 2019, inventory, net was comprised of the following: (In thousands) 2020 2019 Raw materials $ 47,026 $ 36,987 Work in process 776 1,085 Finished goods 77,655 60,233 Total Inventory, net $ 125,457 $ 98,305 Inventory reserves are established for estimated excess and obsolete inventory equal to the difference between the cost of the inventory and the estimated net realizable value of the inventory based on estimated reserve percentages, which consider historical usage, known trends, inventory age and market conditions. As of December 31, 2020 and 2019, our inventory reserve was $39.6 million and $34.1 million, respectively.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property, Plant and Equipment	Note 8 – Property, Plant and Equipment As of December 31, 2020 and 2019, property, plant and equipment, net was comprised of the following: (In thousands) 2020 2019 Land $ 4,575 $ 4,575 Building and land improvements 35,142 34,797 Building 68,169 68,157 Furniture and fixtures 19,965 19,959 Computer hardware and software 70,942 68,777 Engineering and other equipment 132,920 130,430 Total Property, Plant and Equipment 331,713 326,695 Less: accumulated depreciation (269,314 ) (258,609 ) Total Property, Plant and Equipment, net $ 62,399 $ 68,086 Long-lived assets used in operations are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable and the undiscounted cash flows estimated to be generated by the asset are less than the asset’s carrying value. During the years ended December 31, 2020 and December 31, 2019, the Company recognized impairment charges of $0.1 million and $3.9 million, respectively, related to the abandonment of certain information technology projects in which we had previously capitalized expenses related to these projects. The impairment charges were determined based on actual costs incurred as part of the projects. No impairment charges were recognized during the year ended December 31, 2018. Depreciation expense was $12.2 million, $12.5 million and $12.7 million for the years ended December 31, 2020, 2019 and 2018, respectively, which is recorded in cost of sales, selling, general and administrative expenses and research and development expenses in the Consolidated Statements of Income (Loss).

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	Note 9 – Leases We have operating leases for office space, automobiles and various other equipment in the U.S. and in certain international locations. Other contracts, such as manufacturing agreements and service agreements, are reviewed to determine if they contain potential embedded leases. These other contracts are specifically reviewed to determine whether we have the right to substantially all of the economic benefit from the use of any specified assets or the right to direct the use of any specified assets, either of which would indicate the existence of a lease. As of December 31, 2020, our operating leases had remaining lease terms of two months to 55 months, some of which included options to extend the leases for up to two years, and some of which included options to terminate the leases within three months December 31, December 31, (In thousands) Classification 2020 2019 Assets Operating lease assets Other non-current assets $ 5,309 $ 8,452 Total lease asset $ 5,309 $ 8,452 Liabilities Current operating lease liability Accrued expenses and other liabilities $ 1,806 $ 2,676 Non-current operating lease liability Other non-current liabilities 3,574 5,818 Total lease liability $ 5,380 $ 8,494 Leases with an initial term of 12 months or less are not recorded on the balance sheet and lease expense for these leases is recognized on a straight-line basis over the lease term. Lease expense related to these short-term leases was less than $0.1 million and $0.4 million for the year ended December 31, 2020 and 2019, respectively, and is included in cost of sales, selling, general and administrative expenses and research and development expenses in the Consolidated Statements of Income (Loss). Lease expense related to variable lease payments that do not depend on an index or rate, such as real estate taxes and insurance reimbursements, was $0.7 million and $0.9 million for the year ended December 31, 2020 and 2019, respectively. For lease agreements entered into or reassessed after the adoption of Topic 842, we elected to not separate lease and non-lease components. Our lease agreements do not contain any material residual value guarantees or material restrictive covenants. The components of lease expense included in the Consolidated Statements of Income (Loss) were as follows: For the year ended December 31, (In thousands) 2020 2019 Cost of sales $ 113 $ 64 Selling, general and administrative expenses 1,311 1,400 Research and development expenses 1,121 2,417 Total operating lease expense $ 2,545 $ 3,881 As of December 31, 2020, operating lease liabilities included on the Consolidated Balance Sheet by future maturity were as follows: (In thousands) Amount 2021 $ 1,895 2022 1,600 2023 1,251 2024 521 2025 287 Thereafter — Total lease payments 5,554 Less: Interest (174 ) Present value of lease liabilities $ 5,380 Future o perating lease payments include $0.3 million related to options to extend lease terms that are reasonably certain of being exercised. There are no legally binding leases that have not yet commenced An incremental borrowing rate is used based on information available at the commencement date in determining the present value of lease payments. The incremental borrowing rate is determined on a portfolio basis by grouping leases with similar terms as well as grouping leases based on a U.S. dollar or Euro functional currency. The actual rate is then determined based on a credit spread over LIBOR as well as the Bloomberg Curve Matrix for the U.S. Communications section. The following table provides information about our weighted average lease terms and weighted average discount rates: As of December 31, Weighted average remaining lease term (years) 2020 2019 Operating leases with USD functional currency 2.4 2.6 Operating leases with Euro functional currency 3.6 4.4 Weighted average discount rate Operating leases with USD functional currency 4.47 % 4.02 % Operating leases with Euro functional currency 1.37 % 1.84 % Supplemental cash flow information related to operating leases is as follows: As of December 31, (In thousands) 2020 2019 Cash paid for amounts included in the measurement of operating lease assets/liabilities Cash used in operating activities related to operating leases $ 2,632 $ 3,439 Right-of-use assets obtained in exchange for operating lease obligations $ 324 $ 11,615 Sales-Type Leases We are the lessor in sales-type lease arrangements for network equipment, which have initial terms of up to five years. Our sales-type lease arrangements contain either a provision whereby the network equipment reverts back to us upon the expiration of the lease or a provision that allows the lessee to purchase the network equipment at a bargain purchase amount at the end of the lease. In addition, our sales-type lease arrangements do not contain any residual value guarantees or material restrictive covenants. The allocation of the consideration between lease and non-lease components is determined by stand-alone selling price by component. The net investment in sales-type leases consists of lease receivables less unearned income. Collectability of sales-type leases is evaluated periodically at an individual customer level. The Company has elected to exclude taxes related to sales-type leases from revenue and the associated expense of such taxes. As of December 31, 2020 and 2019, we did not have an allowance for credit losses for our net investment in sales-type leases. As of December 31, 2020 and 2019, the components of the net investment in sales-type leases were as follows: As of December 31, (In thousands) 2020 2019 Current minimum lease payments receivable (1) $ 702 $ 1,201 Non-current minimum lease payments receivable (2) 347 889 Total minimum lease payments receivable 1,049 2,090 Less: Current unearned revenue (1) 218 365 Less: Non-current unearned revenue (2) 50 163 Net investment in sales-type leases $ 781 $ 1,562 (1) Included in other receivables on the Consolidated Balance Sheets. (2) Included in other non-current assets on the Consolidated Balance Sheets. Components of gross profit related to sales-type lease recognized at the lease commencement date and interest and dividend income, included in the Consolidated Statements of Income (Loss) for the year ended December 31, 2020 and 2019 were as follows: For the year ended December 31, (In thousands) 2020 2019 Revenue - Network Solutions $ 78 $ 1,723 Cost of sales - Network Solutions 32 675 Gross profit $ 46 $ 1,048 Interest and dividend income $ 42 $ 357 As of December 31, 2020 future minimum lease payments to be received from sales-type leases were as follows: (In thousands) Amount 2021 $ 703 2022 250 2023 88 2024 7 2025 1 Total $ 1,049

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2020
Goodwill Disclosure [Abstract]
Goodwill	Note 10 – Goodwill Goodwill, all of which relates to our acquisitions of Bluesocket, Inc. in 2011 and SmartRG in 2018, was $7.0 million as of December 31, 2020 and December 31, 2019 of which $6.6 million and $0.4 million was allocated to our Network Solutions and Services & Support reportable segments, respectively. The Company evaluates the carrying value of goodwill during the fourth quarter of each year and between annual evaluations if events occur or circumstances change that could more likely than not reduce the fair value of the reporting unit below its carrying amount. We have elected to by-pass a qualitative assessment to determine whether it is more likely than not that the fair value of the reporting unit to which the goodwill is assigned is less than its carrying amount. No impairment charges related to goodwill were recognized during the years ended December 31, 2020, 2019 and 2018.

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2020
Intangible Assets Net Excluding Goodwill [Abstract]
Intangible Assets	Note 11 – Intangible Assets Intangible assets as of December 31, 2020 and 2019, consisted of the following: 2020 2019 (In thousands) Gross Value Accumulated Amortization Net Value Gross Value Accumulated Amortization Net Value Customer relationships $ 21,123 $ (8,055 ) $ 13,068 $ 22,356 $ (7,233 ) $ 15,123 Developed technology 8,200 (2,546 ) 5,654 10,170 (3,379 ) 6,791 Licensed technology 5,900 (1,830 ) 4,070 5,900 (1,174 ) 4,726 Supplier relationships 2,800 (2,800 ) — 2,800 (2,508 ) 292 Licensing agreements 560 (152 ) 408 560 (79 ) 481 Patents 500 (294 ) 206 500 (226 ) 274 Trade names 210 (146 ) 64 310 (176 ) 134 Total $ 39,293 $ (15,823 ) $ 23,470 $ 42,596 $ (14,775 ) $ 27,821 The Company evaluates the carrying value of intangible assets whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable and the undiscounted cash flows estimated to be generated by the asset are less than the asset’s carrying value. No Amortization expense was $4.4 million, $5.3 million and $2.3 million for the years ended December 31, 2020, 2019 and 2018, respectively, and was included in cost of sales, selling, general and administrative expenses and research and development expenses As of December 31, 2020, estimated future amortization expense of intangible assets was as follows: (In thousands) Amount 2021 $ 4,119 2022 3,494 2023 3,340 2024 3,245 2025 3,031 Thereafter 6,241 Total $ 23,470

Revolving Credit Agreement

Revolving Credit Agreement	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Revolving Credit Agreement	Note 12 – Revolving Credit Agreement On November 4, 2020, the Company, as borrower, entered into a Revolving Credit and Security Agreement and related Promissory Note (together, the “Revolving Credit Agreement”) with Cadence Bank, N.A., as lender (the “Lender”). The Revolving Credit Agreement provides the Company with a new $10.0 million secured revolving credit facility. Loans under the Revolving Credit Agreement will bear interest at a rate equal to 1.50% over the screen rate as obtained by Reuter’s, Bloomberg or another commercially available source as may be designated by the Lender from time to time; provided, however, that in no event shall the applicable rate of interest under the Revolving Credit Agreement be less than 1.50% per annum. Such loans are secured by all of the cash, securities, securities entitlements and investment property in a certain bank account, as outlined in the Revolving Credit Agreement, at a maximum loan-to-value ratio of 75% determined by dividing the full commitment amount under the Revolving Credit Agreement on the date of testing, determined by the Lender each fiscal quarter, by the market value of the collateral. The Revolving Credit Agreement matures on November 4, 2021, subject to earlier termination upon the occurrence of certain events of default. The Company had not made any draws under the Revolving Credit Agreement as of December 31, 2020.

Alabama State Industrial Develo

Alabama State Industrial Development Authority Financing and Economic Incentives	12 Months Ended
	Dec. 31, 2020
Text Block [Abstract]
Alabama State Industrial Development Authority Financing and Economic Incentives	Note 13 – Alabama State Industrial Development Authority Financing and Economic Incentives In conjunction with the 1995 expansion of our Huntsville, Alabama facility, we were approved for participation in an incentive program offered by the State of Alabama Industrial Development Authority (the “Authority”). Pursuant to the program, in January 1995, the Authority issued $20.0 million of its taxable revenue bonds (the “Taxable Revenue Bonds”) and loaned the proceeds from the sale of the Taxable Revenue Bonds to the Company . Further advances on the Taxable Revenue Bonds were made by the Authority, bringing the total amount outstanding to $50.0 million. The Taxable Revenue Bonds bore interest, payable monthly with an interest rate of 2% The Taxable Revenue Bonds’ aggregate principal amount outstanding of $24.6 million matured on January 1, 2020 and This certificate of deposit, which totaled $25.6 million, was included in short-term investments on the Consolidated Balance Sheet as of December 31, 2019. We made a principal payment of $1.0 million for the year ended December 31, 2019. In conjunction with this program, we were eligible to receive certain economic incentives from the state of Alabama that reduce the amount of payroll withholdings that we were required to remit to the state for those employment positions that qualify under the program. Economic incentives realized related to payroll withholdings totaled $0, $1.2 million and $1.4 million for the years ended December 31, 2020, 2019 and 2018, respectively. This program concluded on January 2, 2020 following the maturity of the Taxable Revenue Bonds.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Note 14 – Income Taxes The components of income tax expense (benefit) for the years ended December 31, 2020, 2019 and 2018 are as follows: (In thousands) 2020 2019 2018 Current Federal $ (10,574 ) $ (518 ) $ (8,001 ) State (329 ) (1,065 ) (476 ) International 3,635 (282 ) 11,705 Total Current (7,268 ) (1,865 ) 3,228 Deferred Federal — 24,801 (14,448 ) State — 5,815 (3,390 ) International (1,356 ) (546 ) 581 Total Deferred (1,356 ) 30,070 (17,257 ) Total Income Tax Expense (Benefit) $ (8,624 ) $ 28,205 $ (14,029 ) The effective income tax rate differs from the federal statutory rate due to the following: 2020 2019 2018 Tax provision computed at the federal statutory rate 21.00 % 21.00 % 21.00 % State income tax provision, net of federal benefit 11.10 6.97 14.53 Federal research credits 57.63 15.53 14.23 Foreign taxes (17.83 ) 2.83 (11.45 ) Tax-exempt income 1.93 0.49 0.45 State tax incentives — 3.85 3.15 Change in valuation allowance 44.79 (172.82 ) — Foreign tax credits 17.90 16.69 — Stock-based compensation (23.36 ) (6.01 ) (2.87 ) Withholding taxes (20.83 ) — — Bargain purchase — — 8.82 Impact of CARES Act 45.65 — — Impact of U.S. tax reform — — 12.00 Global intangible low-taxed income ("GILTI") (0.49 ) (1.87 ) (17.48 ) Other, net 0.56 (0.49 ) (0.34 ) Effective Tax Rate 138.05 % (113.83 )% 42.04 % Income (loss) before expense (benefit) for income taxes for the years ended December 31, 2020, 2019 and 2018 is as follows: (In thousands) 2020 2019 2018 U.S. entities $ (12,833 ) $ (29,829 ) $ (74,131 ) International entities 6,587 5,052 40,760 Total $ (6,246 ) $ (24,777 ) $ (33,371 ) Income (loss) before expense (benefit) for income taxes for international entities reflects income (loss) based on statutory transfer pricing agreements. This amount does not correlate to consolidated international revenue, which occurs from our U.S. entity. Deferred income taxes on the Consolidated Balance Sheets result from temporary differences between the amount of assets and liabilities recognized for financial reporting and tax purposes. The significant components of current and non-current deferred taxes as of December 31, 2020 and 2019 consist of the following: (In thousands) 2020 2019 Deferred tax assets: Inventory $ 8,882 $ 7,144 Accrued expenses 2,331 2,330 Deferred compensation 6,714 5,660 Stock-based compensation 1,971 2,451 Uncertain tax positions related to state taxes and related interest 149 241 Pensions 8,554 7,074 Foreign losses 2,590 2,925 State losses and credit carry-forwards 5,509 3,995 Federal loss and research carry-forwards 17,323 12,171 Lease liabilities 1,588 2,496 Capitalized research and development expenditures 11,832 22,230 Valuation allowance (45,818 ) (48,616 ) Total Deferred Tax Assets 21,625 20,101 Deferred tax liabilities: Property, plant and equipment (4,546 ) (2,815 ) Intellectual property (4,375 ) (5,337 ) Right of use lease assets (1,585 ) (2,496 ) Investments (1,250 ) (1,892 ) Total Deferred Tax Liabilities (11,756 ) (12,540 ) Net Deferred Tax Assets $ 9,869 $ 7,561 On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”) was signed into law. Subsequently, the Internal Revenue Service (“IRS”) released its final Global Intangible Low Tax Income (“GILTI”) regulations on July 9, As of December 31, 2020 and 2019, non-current deferred taxes reflect deferred taxes on net unrealized gains and losses on available-for-sale investments and deferred taxes on unrealized losses in our pension plan. The net change in non-current deferred taxes associated with these items, which resulted in a deferred tax benefit of $0.1 million and $0.4 million in 2020 and 2019, respectively, was recorded as an adjustment to other comprehensive income (loss), presented in the Consolidated Statements of Comprehensive Income (Loss). The Company continually reviews the adequacy of its valuation allowance and recognizes the benefits of deferred tax assets only as the reassessment indicates that it is more likely than not that the deferred tax assets will be recognized in accordance with ASC 740, Income Taxes. As of December 31, 2020 and 2019, the Company had gross deferred tax assets totaling $55.7 million offset by a valuation allowance totaling $45.8 million and gross deferred tax assets totaling $56.2 million offset by a valuation allowance of $48.6 million, respectively. Of the current valuation allowance, $43.8 million has been established against our domestic deferred tax assets and the remaining $2.0 million is related to foreign net operating loss and research and development credit carryforwards where we lack sufficient activity to realize those deferred tax assets. The change in our valuation allowance for the year ending December 31, 2020 was a decrease of $2.8 million. The change in the valuation allowance was primarily related to increases in our deferred tax assets during the year, offset with the impact of monetizing deferred tax assets through net operating loss carryback claims related to the CARES Act of $7.9 million. As of December 31, 2020, the remaining $9.9 million in deferred tax assets that were not offset by a valuation allowance are located in various foreign jurisdictions where the Company believes it is more likely than not we will realize these deferred tax assets. Supplemental balance sheet information related to deferred tax assets as of December 31, 2020 and 2019 is as follows: December 31, 2020 (In thousands) Deferred Tax Assets Valuation Allowance Deferred Tax Assets, net Domestic $ 43,791 $ (43,791 ) $ — International 11,896 (2,027 ) 9,869 Total $ 55,687 $ (45,818 ) $ 9,869 December 31, 2019 (In thousands) Deferred Tax Assets Valuation Allowance Deferred Tax Assets, net Domestic $ 46,266 $ (46,266 ) $ — International 9,911 (2,350 ) 7,561 Total $ 56,177 $ (48,616 ) $ 7,561 As of December 31, 2020 and 2019, the deferred tax assets for foreign and domestic loss carry-forwards, research and development tax credits, unamortized research and development costs and state credit carry-forwards totaled $37.3 million and $41.3 million, respectively. As of December 31, 2020, $25.1 million of these deferred tax assets will expire at various times between 2021 and 2040. The remaining deferred tax assets will either amortize through 2029 or carryforward indefinitely. As of December 31, 2020 and 2019, respectively, our cash and cash equivalents were $60.2 million and $73.8 million and short-term investments were $3.1 million and $33.2 million, which provided available short-term liquidity of $63.3 million and $107.0 million. Of these amounts, our foreign subsidiaries held cash of $49.7 million and $52.3 million, respectively, representing approximately 78.5% and 48.9% of available short-term liquidity, which is used to fund ongoing liquidity needs of these subsidiaries. As part of our restructuring plan, the Company’s assertion on being indefinitely reinvested changed in a particular jurisdiction during the current year resulting in the accrual of $0.7 million in withholding tax liabilities. The Company maintains its assertion in all other jurisdictions that it is indefinitely reinvesting its funds held in foreign jurisdictions outside of the U.S., except to the extent any of these funds can be repatriated without withholding tax. However, if all of these funds were repatriated to the U.S., or used for U.S. operations, certain amounts could be subject to tax. Due to the timing and circumstances of repatriation of such earnings, if any, it is not practicable to determine the amount of funds subject to unrecognized deferred tax liability. During 2020, 2019 and 2018, no income tax benefit or expense was recorded for stock options exercised as an adjustment to equity. The change in the unrecognized income tax benefits for the years ended December 31, 2020, 2019 and 2018 is reconciled below: (In thousands) 2020 2019 2018 Balance at beginning of period $ 1,487 $ 1,868 $ 2,366 Increases for tax position related to: Prior years 4 — 3 Current year 165 161 254 Decreases for tax positions related to: Prior years — (71 ) — Expiration of applicable statute of limitations (578 ) (471 ) (755 ) Balance at end of period $ 1,078 $ 1,487 $ 1,868 As of December 31, 2020, 2019 and 2018, our total liability for unrecognized tax benefits was $1.1 million, $1.5 million and $1.9 million, respectively, of which $1.0 million, $1.4 million and $1.7 million, respectively, would reduce our effective tax rate if we were successful in upholding all of the uncertain positions and recognized the amounts recorded. We classify interest and penalties recognized on the liability for unrecognized tax benefits as income tax expense. As of December 31, 2020, 2019 and 2018, the balances of accrued interest and penalties were $0.3 million, $0.5 million and $0.7 million, respectively. We do not anticipate a single tax position generating a significant increase or decrease in our liability for unrecognized tax benefits within 12 months of this reporting date. We file income tax returns in the U.S. for federal and various state jurisdictions and several foreign jurisdictions. We are not currently under audit by the Internal Revenue Service. Generally, we are not subject to changes in income taxes by any taxing jurisdiction for the years prior to 2017.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plans	Note 15 – Employee Benefit Plans Pension Benefit Plan We maintain a defined benefit pension plan covering employees in certain foreign countries. The pension benefit plan obligations and funded status as of December 31, 2020 and 2019, were as follows: (In thousands) 2020 2019 Change in projected benefit obligation: Projected benefit obligation at beginning of period $ 43,902 $ 37,245 Service cost 1,270 1,471 Interest cost 444 634 Actuarial (gain) loss - experience (744 ) 453 Actuarial loss - assumptions 2,458 5,091 Benefit payments (509 ) (166 ) Effects of foreign currency exchange rate changes 4,106 (826 ) Projected benefit obligation at end of period 50,927 43,902 Change in plan assets: Fair value of plan assets at beginning of period 28,016 24,159 Actual gain on plan assets 1,744 4,392 Contributions 24 — Effects of foreign currency exchange rate changes 2,479 (535 ) Fair value of plan assets at end of period 32,263 28,016 Unfunded status at end of period $ (18,664 ) $ (15,886 ) The accumulated benefit obligation was $50.9 million and $43.9 million as of December 31, 2020 and 2019, respectively. The increase in the accumulated benefit obligation, projected benefit obligation and the actuarial loss was primarily attributable to a decrease in the discount rate during 2020. The net amounts recognized in the Consolidated Balance Sheets for the unfunded pension liability as of December 31, 2020 and 2019 were as follows: (In thousands) 2020 2019 Current liability $ — $ — Pension liability 18,664 15,886 Total $ 18,664 $ 15,886 The components of net periodic pension cost, other than the service cost component, are included in other income (expense), net in the Consolidated Statements of Income (Loss). The components of net periodic pension cost and amounts recognized in other comprehensive income (loss) for the years ended December 31, 2020, 2019 and 2018 were as follows: (In thousands) 2020 2019 2018 Net periodic benefit cost: Service cost $ 1,270 $ 1,471 $ 1,193 Interest cost 444 634 727 Expected return on plan assets (1,679 ) (1,392 ) (1,548 ) Amortization of actuarial losses 970 795 247 Net periodic benefit cost 1,005 1,508 619 Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss): Net actuarial (gain) loss 1,784 2,488 5,638 Amortization of actuarial losses (1,212 ) (771 ) (196 ) Amount recognized in other comprehensive income (loss) 572 1,717 5,442 Total recognized in net periodic benefit cost and other comprehensive income (loss) $ 1,577 $ 3,225 $ 6,061 The amounts recognized in accumulated other comprehensive income (loss) as of December 31, 2020 and 2019 were as follows: (In thousands) 2020 2019 Net actuarial loss $ (13,545 ) $ (12,973 ) The defined benefit pension plan is accounted for on an actuarial basis, which requires the use of various assumptions, including an expected rate of return on plan assets and a discount rate. The expected return on our German plan assets that is utilized in determining the benefit obligation and net periodic benefit cost is derived from periodic studies, which include a review of asset allocation strategies, anticipated future long-term performance of individual asset classes, risks using standard deviations and correlations of returns among the asset classes that comprise the plans' asset mix. While the studies give appropriate consideration to recent plan performance and historical returns, the assumptions are primarily long-term, prospective rates of return. The discount rate has been derived from the returns of high-quality, corporate bonds denominated in Euro currency with durations close to the duration of our pension obligations. The weighted-average assumptions that were used to determine the net periodic benefit cost for the years ended December 31, 2020, 2019 and 2018 were as follows: 2020 2019 2018 Discount rate 1.00 % 1.75 % 2.13 % Rate of compensation increase 2.00 % 2.00 % 2.00 % Expected long-term rates of return 5.90 % 5.90 % 5.90 % The weighted-average assumptions that were used to determine the benefit obligation as of December 31, 2020 and 2019: 2020 2019 Discount rate 0.69 % 1.00 % Rate of compensation increase 2.00 % 2.00 % Actuarial gains and losses are recorded in accumulated other comprehensive income (loss). To the extent unamortized gains and losses exceed 10% of the higher of the market-related value of assets or the projected benefit obligation, the excess is amortized as a component of net periodic pension cost over the remaining service period of active participants. We do not anticipate making any contributions to the pension plan in 2021. The following pension benefit payments, which reflect expected future service, as appropriate, are expected to be paid to participants: (In thousands) 2021 $ 714 2022 1,048 2023 1,348 2024 1,657 2025 1,621 2026 - 2030 7,615 Total $ 14,003 U.S. GAAP establishes a three-level valuation hierarchy based upon observable and unobservable inputs for fair value measurement of financial instruments: • Level 1 – Observable outputs; values based on unadjusted quoted prices for identical assets or liabilities in an active market; • Level 2 – Significant inputs that are observable; values based on quoted prices in markets that are not active or model inputs that are observable either directly or indirectly; • Level 3 – Significant unobservable inputs; values based on prices or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement. These inputs could include information supplied by investees. We have categorized our cash equivalents and our investments held at fair value into this hierarchy as follows: Fair Value Measurements at December 31, 2020 Using (In thousands) Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents $ 1,935 $ 1,935 $ — $ — Available-for-sale securities Bond funds: Corporate bonds 6,746 6,746 — — Government bonds 5,971 5,971 — — Emerging markets bonds 307 307 — — Equity funds: Global equity 11,638 11,638 — — Balanced fund 2,515 2,515 — — Emerging markets 1,848 1,848 — — Large cap value 198 198 — — Global real estate fund 799 799 — — Managed futures fund 306 306 — — Available-for-sale securities 30,328 30,328 — — Total $ 32,263 $ 32,263 $ — $ — Fair Value Measurements at December 31, 2019 Using (In thousands) Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents $ 691 $ 691 $ — $ — Available-for-sale securities Bond funds: Government bonds 6,645 6,645 — — Corporate bonds 5,514 5,514 — — Emerging markets bonds 531 531 — — Equity funds: Global equity 11,071 11,071 — — Emerging markets 956 956 — — Balanced fund 863 863 — — Large cap value 312 312 — — Global real estate fund 902 902 — — Managed futures fund 531 531 — — Available-for-sale securities 27,325 27,325 — — Total $ 28,016 $ 28,016 $ — $ — Our investment policy includes various guidelines and procedures designed to ensure assets are invested in a manner necessary to meet expected future benefits earned by participants and consider a broad range of economic conditions. Central to the policy are target allocation ranges by asset class, which is currently 50% for bond funds, 40% for equity funds and 10% for cash, real estate and managed futures. The objectives of the target allocations are to maintain investment portfolios that diversify risk through prudent asset allocation parameters, achieve asset returns that meet or exceed the plans’ actuarial assumptions and achieve asset returns that are competitive with like institutions employing similar investment strategies. The investment policy is periodically reviewed by us and a designated third-party fiduciary for investment matters. The policy is established and administered in a manner that is compliant at all times with applicable government regulations. 401(k) Savings Plan We maintain the ADTRAN, Inc. 401(k) Retirement Plan (the “Savings Plan”) for the benefit of eligible employees. The Savings Plan is intended to qualify under Sections 401(a) and 401(k) of the Internal Revenue Code of 1986, as amended (the “Code”), and is intended to be a “safe harbor” 401(k) plan under Code Section 401(k)(12). The Savings Plan allows employees to save for retirement by contributing part of their compensation to the plan on a tax-deferred basis. The Savings Plan also requires us to contribute a “safe harbor” amount each year. We match up to 4% of employee contributions (100% of an employee’s first 3% of contributions and 50% of their next 2% of contributions), beginning on the employee’s one-year anniversary date. In calculating our matching contribution, compensation up to the statutory maximum under the Code is used ($285,000 for 2020). All matching contributions under the Savings Plan vest immediately. Employer contribution expense and plan administration costs for the Savings Plan amounted to approximately $4.0 million, $4.4 million and $4.4 million in 2020, 2019 and 2018, respectively. Deferred Compensation Plans We maintain four deferred compensation programs for certain executive management employees and our Board of Directors. The ADTRAN, Inc. Deferred Compensation Program for Employees is offered as a supplement to our tax-qualified 401(k) plan and is available to certain executive management employees who have been designated by our Board of Directors. This deferred compensation plan allows participants to defer all or a portion of certain specified bonuses and up to 25% of remaining cash compensation and permits us to make matching contributions on a discretionary basis without the limitations that apply to the 401(k) plan. To date, we have not made any matching contributions under this plan. We also maintain the ADTRAN, Inc. Equity Deferral Program for Employees. Under this plan, participants may elect to defer all or a portion of their vested PSUs and RSUs to the plan. Such deferrals shall continue to be held and deemed to be invested in shares of ADTRAN stock unless and until the amounts are distributed or such deferrals are moved to another deemed investment pursuant to an election made by the participant. For our Board of Directors, we maintain the ADTRAN, Inc. Deferred Compensation Program for Directors. This program allows our Board of Directors to defer all or a portion of monetary remuneration paid to the Director, including, but not limited to, meeting fees and annual retainers. We also maintain the ADTRAN, Inc. Equity Deferral Program for Directors. Under this plan, participants may elect to defer all or a portion of their vested restricted stock awards. Such deferrals shall continue to be held and deemed to be invested in shares of ADTRAN stock unless and until the amounts are distributed or such deferrals are moved to another deemed investment pursuant to an election made by the director. We have set aside the plan assets for all plans in a rabbi trust (the “Trust”) and all contributions are credited to bookkeeping accounts for the participants. The Trust assets are subject to the claims of our creditors in the event of bankruptcy or insolvency. The assets of the Trust are deemed to be invested in pre-approved mutual funds as directed by each participant and the participant’s bookkeeping account is credited with the earnings and losses attributable to those investments. Benefits are scheduled to be distributed six months after termination of employment in a single lump sum payment or annual installments paid over a three or ten-year Assets of the Trust are deemed invested in mutual funds that cover an investment spectrum ranging from equities to money market instruments. These mutual funds are publicly quoted and reported at fair value. The fair value of the assets held by the Trust and the amounts payable to the plan participants as of December 31, 2020 and 2019 were as follows: (In thousands) 2020 2019 Fair Value of Plan Assets Long-term investments $ 23,891 $ 21,698 Total Fair Value of Plan Assets $ 23,891 $ 21,698 Amounts Payable to Plan Participants Deferred compensation liability $ 25,866 $ 21,698 Total Amounts Payable to Plan Participants $ 25,866 $ 21,698 The Trust held $2.8 million of common stock in the Company as of December 31, 2020. Shares of the Company held by the Trust are recorded at cost and classified as treasury stock on the Consolidated Balance Sheet. Interest and dividend income of the Trust are included in interest and dividend income in the accompanying 2020, 2019 and 2018 Consolidated Statements of Income (Loss). Changes in the fair value of the plan assets held by the Trust have been included in other income (expense) in the accompanying 2020, 2019 and 2018 Consolidated Statements of Income (Loss). Changes in the fair value of the deferred compensation liability are included as selling, general and administrative expense in the accompanying 2020, 2019 and 2018 Consolidated Statements of Income (Loss). Based on the changes in the total fair value of the Trust’s assets, we recorded deferred compensation income (expense) in 2020, 2019 and 2018 of $4.3 million, $3.6 million and $(2.1) million, respectively. Retiree Medical Coverage Medical, dental and prescription drug coverage is provided to certain spouses and former spouses of current and former officers on the same terms as provided to our active officers for up to 30 years. As of December 31, 2020 and 2019, this liability totaled $0.2 million and $0.1 million, respectively.

Segment Information and Major C

Segment Information and Major Customers	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Segment Information and Major Customers	Note 16 – Segment Information and Major Customers The chief operating decision maker regularly reviews the Company’s financial performance based on two reportable segments: (1) Network Solutions and (2) Services & Support. Network Solutions includes hardware products and software defined next-generation virtualized solutions used in service provider or business networks, as well as prior-generation products. Services & Support includes a portfolio of maintenance, network implementation and solutions integration and managed services, which include hosted cloud services and subscription services. The performance of each segment is evaluated based on gross profit; therefore, selling, general and administrative expenses, research and development expenses, interest and dividend income, interest expense, net investment gain (loss), other income (expense) and income tax (expense) benefit are reported on a Company-wide basis only. There is no inter-segment revenue. Asset information by reportable segment is not produced and, therefore, is not reported. The following table presents information about revenue and gross profit of our reportable segments for each of the years ended December 31, 2020, 2019 and 2018: 2020 2019 2018 (In thousands) Revenue Gross Profit Revenue Gross Profit Revenue Gross Profit Network Solutions $ 438,015 $ 193,789 $ 455,226 $ 191,549 $ 458,232 $ 179,303 Services & Support 68,495 23,762 74,835 27,618 71,045 24,262 Total $ 506,510 $ 217,551 $ 530,061 $ 219,167 $ 529,277 $ 203,565 Revenue by Category In addition to our reportable segments, revenue is also reported for the following three categories – (1) Access & Aggregation, (2) Subscriber Solutions & Experience and (3) Traditional & Other Products. The following tables disaggregate our revenue by category for the years ended December 31, 2020, 2019 and 2018: 2020 (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 262,578 $ 50,560 $ 313,138 Subscriber Solutions & Experience 161,824 9,263 171,087 Traditional & Other Products 13,613 8,672 22,285 Total $ 438,015 $ 68,495 $ 506,510 2019 (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 289,980 $ 58,894 $ 348,874 Subscriber Solutions & Experience 144,651 8,269 152,920 Traditional & Other Products 20,595 7,672 28,267 Total $ 455,226 $ 74,835 $ 530,061 2018 (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 301,801 $ 57,069 $ 358,870 Subscriber Solutions & Experience 129,067 5,393 134,460 Traditional & Other Products 27,364 8,583 35,947 Total $ 458,232 $ 71,045 $ 529,277 Additional Information The following table presents revenue information by geographic area for the years ended December 31, 2020, 2019 and 2018: (In thousands) 2020 2019 2018 United States $ 352,079 $ 300,853 $ 288,843 Germany 74,882 78,062 167,251 Mexico 4,087 90,795 12,186 Other international 75,462 60,351 60,997 Total $ 506,510 $ 530,061 $ 529,277 Customers comprising more than 10% of revenue can change from year to year. Single customers comprising more than 10% of revenue in 2020 included three customers, at 15%, 12% and 10%, of which one was a distributor. Single customers comprising more than 10% of revenue in 2019 included three customers at 19%, 17% and 13%. Single customers comprising more than 10% of revenue in 2018 included two customers at 27% and 17%. Other than those with more than 10% of revenues disclosed above, and excluding distributors, our next five largest customers can change, and have historically changed, from year-to-year. The next five largest customers combined represented 19%, 15% and 18% of total revenue in 2020, 2019 and 2018, respectively. As of December 31, 2020, property, plant and equipment, net totaled $62.4 million, which included $58.4 million held in the U.S. and $4.0 million held outside the U.S. As of December 31, 2019, property, plant and equipment, net totaled $68.1 million, which included $64.2 million held in the U.S. and $3.9 million held outside the U.S. Property, plant and equipment, net is reported on a Company-wide, functional basis only.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 17 – Commitments and Contingencies Securities Class Action Lawsuit On October 17, 2019, a purported stockholder class action lawsuit, captioned Burbridge v. ADTRAN, Inc. et al., Docket No. 19-cv-09619, was filed in the United States District Court for the Southern District of New York against the Company, two of its current executive officers and one of its former executive officers. The complaint alleges violations of federal securities laws and seeks unspecified compensatory damages on behalf of purported purchasers of ADTRAN securities between February 28, 2019 and October 9, 2019. The lawsuit claims that the defendants made materially false and misleading statements regarding, and/or failed to disclose material adverse facts about, the Company’s business, operations and prospects, specifically relating to the Company’s internal control over financial reporting, excess and obsolete inventory reserves, financial results and demand from certain customers. The lawsuit was transferred to the U.S. District Court for the Northern District of Alabama on January 7, 2020, and co-lead plaintiffs have been appointed to represent the putative class. The plaintiffs filed an amended complaint on April 30, 2020. The defendants filed a motion to dismiss the amended complaint on June 17, 2020. The p We deny the allegations in the complaint, as amended, and intend to vigorously defend against this lawsuit. At this time, we are unable to predict the outcome of or estimate the possible loss or range of loss, if any, associated with this lawsuit. Shareholder Derivative Lawsuit On March 31, 2020, a shareholder derivative suit, captioned Johnson (Derivatively on behalf of ADTRAN) v. T. Stanton, M. Foliano, R. Shannon, and Board of Directors and its defendants disagree with the claims made in the complaint, and the defendants intend to vigorously defend against this lawsuit. At this time, we are unable to predict the outcome of or estimate the possible loss or range of loss, if any, associated with this lawsuit. Other Legal Matters In addition to the litigation described above, from time to time we are subject to or otherwise involved in various lawsuits, claims, investigations and legal proceedings that arise out of or are incidental to the conduct of our business (collectively, “Legal Matters”), including those relating to employment matters, patent rights, regulatory compliance matters, stockholder claims, and contractual and other commercial disputes. Such Legal Matters, even if not meritorious, could result in the expenditure of significant financial and managerial resources. Additionally, an unfavorable outcome in any legal matter, including in a patent dispute, could require the Company to pay damages, entitle claimants to other relief, such as royalties, or could prevent the Company from selling some of its products in certain jurisdictions. While the Company cannot predict with certainty the results of the Legal Matters in which it is currently involved, the Company does not expect that the ultimate outcome of such Legal Matters will individually or in the aggregate have a material adverse effect on its business, results of operations, financial condition or cash flows. Performance Bonds Certain contracts, customers and/or jurisdictions in which we do business require us to provide various guarantees of performance such as bid bonds, performance bonds and customs bonds. As of December 31, 2020, we had commitments related to these bonds totaling $15.2 million which expire at various dates through August 2024. As of December 31, 2019, we had commitments related to these bonds totaling $9.3 million. Although the triggering events vary from contract to contract, in general we would only be liable for the amount of these guarantees in the event of default under each contract, the probability of which we believe is remote. In June 2020, the Company entered into a letter of credit with a bank to guarantee performance obligations under a contract with a certain customer. The obligations under this customer contract will be performed over multiple years. As of December 31, 2020, the Company was required to maintain a minimum collateral value of $9.0 million. The letter of credit was secured by a pledge of a portion of the Company’s fixed-income securities, which totaled $11.2 million as of December 31, 2020, of which less than $0.1 million is included in restricted cash and $11.2 million is included in long-term investments on the Consolidated Balance Sheet. This pledged collateral value will fluctuate as the Company changes the mix of the pledged collateral between restricted cash and investments. We expect to reach the maximum value of our minimum collateral requirement of $15.0 million in the first quarter of 2021 as the Company reaches certain milestones through the first quarter of 2021 as outlined in the customer contract. Investment Commitment We have committed to invest up to an aggregate of $5.0 million in a private equity fund, of which $4.9 million has been applied to these commitments as of December 31, 2020.

Current Expected Credit Losses

Current Expected Credit Losses	12 Months Ended
	Dec. 31, 2020
Credit Loss [Abstract]
Current Expected Credit Losses	Note 18 – Current Expected Credit Losses Under ASC 326 – Financial Instruments – Credit Losses Assets Measured at Amortized Cost Accounts Receivable The Company records accounts receivable in the normal course of business as products are shipped or services are performed and invoiced, but payment has not yet been remitted by the customer. Accounts receivable balances are considered past due when payment has not been received by the date indicated on the relevant invoice or based on agreed upon terms between the customer and the Company. As of December 31, 2020 and January 1, 2020 (the “implementation date”) , the Company’s net outstanding accounts receivable balance was $ 98.8 million and $ 90.5 million, respectively. The Company assessed the need for an allowance for credit losses related to its outstanding accounts receivable as of December 31, 2020 and January 1, 2020 using the historical loss-rate method as well as assessing asset-specific risks. The Company’s historical losses related to accounts receivable have been immaterial as evidenced by its historical allowance and write-offs due to uncollectability. The assessment of asset-specific risks included the evaluation of relevant available information, from internal and external sources, relating to current conditions that may affect a customer’s ability to pay, such as the customer’s current financial condition, credit rating by geographic location, as provided by a third party and/or by customer, if needed, and overall macro-economic conditions in which the customer operates. The Company pooled assets by geographic location to determine if an allowance should be applied to its accounts receivable balance, assessing the specific country risk rating and overall economics of that particular country. If elevated risk existed, or customer specific risk indicated the accounts receivable balance was at risk, the Company further analyzed the need for an allowance related to specific accounts receivable balances. Additionally, the Company determined that significant changes to customer country risk rating from period-to-period and from the end of the prior year to the end of the current quarter would require further review and analysis by the Company. No allowance for credit loss was recorded for the year ended December 31, 2020 or on January 1, 2020 related to accounts receivable. The Company’s allowance for credit losses related to accounts receivable was less than $ 0.1 million Contract Assets The Company records contract assets when it has recognized revenue but has not yet billed the customer. As of December 31, 2020 and January 1, 2020, the Company’s outstanding contract asset balance was $0.1 million and $2.8 million, respectively, which is included in other receivables on the Consolidated Balance Sheets as of December 31, 2020 and December 31, 2019. The Company assessed the need for an allowance for credit losses related to its outstanding contract assets as of December 31, 2020 and January 1, 2020 using the historical loss-rate method as well as asset-specific risks. The Company’s historical losses related to contract assets receivable have been immaterial as evidenced by historical write-offs due to uncollectability. Asset-specific risk included the evaluation of relevant available information, from internal and external sources, relating to current conditions that may affect a customer’s ability to pay once invoiced, such as the customer’s financial condition, credit rating by geographic location as provided by a third party and/or by customer, if needed, and overall macro-economic conditions in which the customer operates. The Company pooled assets by geographic location to determine if an allowance should be applied to its contract asset balance, assessing the specific country risk rating and overall economics of that particular country. If elevated risk existed, or customer specific risk indicated the contract balance was at risk, the Company further analyzed the need for an allowance related to specific customer balances. Additionally, the Company determined that significant changes to customer country risk rating from period-to-period and from the end of the prior year to the end of the current quarter would be subject to further review and analysis by the Company. No allowance for credit loss was recorded for the year ended December 31, 2020 or on the implementation date related to contract assets. Net Investment in Sales-Type Leases The Company is the lessor in sales-type lease arrangements for network equipment. As of December 31, 2020 and January 1, 2020, the Company’s outstanding net investment in sales-type leases was $0.8 million and $1.6 million, respectively, which is included in other receivables and other non-current assets on the Consolidated Balance Sheets as of December 31, 2020 and 2019. The Company assessed the need for an allowance for credit losses related to future receivables under its outstanding sales-type leases as of December 31, 2020 and January 1, 2020 using the historical loss-rate method as well as asset-specific risks. The Company’s historical losses related to contract assets receivable have been immaterial as evidenced by historical write-offs due to uncollectability. Asset-specific risk included the evaluation of relevant available information, from internal and external sources, relating to current conditions that may affect a customer’s ability to pay once invoiced, such as the customer’s financial condition, credit rating by geographic location as provided by a third party and/or by customer, if needed, and overall macro-economic conditions in which the customer operates. The following table presents amortized cost basis in sales-type leases based on payment activity: Sales-Type Leases Amortized Cost Basis by Origination Year (In thousands) 2020 2019 2018 2017 2016 Prior Total Payment performance Performing $ 55 $ 192 $ 354 $ 128 $ 52 $ — $ 781 Non-performing — — — — — — — Total $ 55 $ 192 $ 354 $ 128 $ 52 $ — $ 781 Sales-type lease receivables are considered past due when payment has not been received based on agreed upon terms between the customer and the Company. No allowance for credit loss was recorded for the year ended December 31, 2020 or on the implementation date related to sales-type leases. Secured Loan Receivable The Company has a secured loan receivable totaling $0.9 million as of December 31, 2020 and January 1, 2020, which originated in February 2019, and is included in long-term investments on the Consolidated Balance Sheets as of December 31, 2020 and 2019. The Company assessed the need for an allowance for credit loss related to its secured loan receivable as of December 31, 2020 and January 1, 2020 using the historical loss-rate method as well as asset-specific risks. There have been no historical losses related to this receivable. Asset-specific risks included the evaluation of relevant available information, from internal and external sources, relating to current conditions that may affect the customer’s ability to repay the loan upon maturity, such as the customer’s current financial condition, credit rating specific to the customer as determined by a third party and current overall economic conditions, as well as a Company valuation prepared by a third party which was based on reasonable and supportable forecasts as provided by management. Accrued interest receivable on the secured loan receivable, which is included in other receivables on the Consolidated Balance Sheets totaled less than $ 0.1 million No allowance for credit loss was recorded for the year ended December 31, 2020 or on the implementation date related to the secured loan receivable. Off-Balance Sheet Arrangements The Company did not have any off-balance sheet arrangements as of December 31, 2020 or January 1, 2020. As of December 31, 2020 and January 1, 2020, the Company’s available-for-sale debt securities totaled $45.1 million and $37.7 million, respectively. These securities were analyzed at the individual investment level, by Committee on Uniform Securities Identification Procedures (“CUSIP”), to limit credit losses, if applicable, to reflect only the amount by which the fair value of the security was less than its amortized cost. The Company noted that, as of December 31, 2020 and January 1, 2020, there was no intent to sell any of its available-for-sale debt securities before maturity, and, therefore, the Company assessed the need for an allowance for each of its available-for-sale debt securities in which the fair value was less than its amortized cost as of December 31, 2020 and January 1, 2020. The Company had 42 positions in available-for-sale debt securities that were in an unrealized loss position as of December 31, 2020. See Note 6 of Notes to Consolidated Financial Statements included in Part II, Item 8 of this report for additional information. For those available-for-sale debt securities whose fair value was less than its amortized cost basis, the Company analyzed additional criteria such as adverse conditions specifically related to the security, an industry or geographic area, failure of the issuer of the security to make scheduled interest or principal payments, if applicable, and any changes to the rating of the security by a rating agency to determine if a credit loss existed. The Company used information provided by its investment manager to determine if any scheduled interest or principal payments had not been received and used a third party to determine if any changes to credit ratings had occurred. The Company noted that all principal and interest payments had been received as scheduled and that there had been no changes in credit ratings year-over-year or period-over-period that warranted further review. No allowance for credit loss was recorded for the year ended December 31, 2020 or on the implementation date related to the Company’s available-for-sale debt securities.

Earnings (Loss) Per Share

Earnings (Loss) Per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Earnings (Loss) Per Share	Note 19 – Earnings (Loss) per Share The calculations of basic and diluted earnings (loss) per share for the years ended December 31, 2020, 2019 and 2018 are as follows: (In thousands, except for per share amounts) 2020 2019 2018 Numerator Net Income (Loss) $ 2,378 $ (52,982 ) $ (19,342 ) Denominator Weighted average number of shares – basic 47,996 47,836 47,880 Effect of dilutive securities: Stock options — — — PSUs, RSUs and restricted stock 292 — — Weighted average number of shares – diluted 48,288 47,836 47,880 Earnings (loss) per share – basic $ 0.05 $ (1.11 ) $ (0.40 ) Earnings (loss) per share – diluted $ 0.05 $ (1.11 ) $ (0.40 ) For the years ended December 31, 2020 and 2019, 0.1 million and 0.5 million shares, respectively, of unvested or unearned, as applicable, PSUs, RSUs and restricted stock were excluded from the calculation of diluted earnings per share due to their anti-dilutive effect. For the year ended December 31, 2020 and 2019, 3.6 million and 5.2 million stock options were outstanding but were not included in the computation of diluted earnings per share due to the fact that their exercise prices were greater than the average market price of the common shares during the quarter, making them anti-dilutive under the treasury stock method.

Restructuring

Restructuring	12 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Restructuring	Note 20 – Restructuring During the second half of 2019, the Company initiated a restructuring plan to realign its expense structure with the reduction in revenue experienced in recent years and overall Company objectives. As part of this restructuring plan, the Company announced plans to reduce its overall operating expenses, both in the U.S. and internationally. Management continued to assess the efficiency of operations during 2020 and, in turn, consolidated locations and personnel, among other things, where possible. In February 2019, the Company announced the restructuring of a certain portion of its workforce predominantly in Germany, which included the closure of the Company’s office location in Munich, Germany accompanied by relocation or severance benefits for the affected employees. Voluntary early retirement was offered to certain other employees and was announced in March 2019 and again in August 2020. The cumulative amount of restructuring expenses incurred as of December 31, 2020 for the restructuring plans announced in the second half of 2019 and continuing in 2020 was $12.2 million. In January 2018, the Company announced an early retirement incentive program for employees that met certain defined requirements. The cumulative amount incurred during the year ended December 31, 2018 related to this restructuring program was $7.3 million. We did not incur any additional expenses related to this restructuring program during the year ended December 31, 2019 or 2020. A reconciliation of the beginning and ending restructuring liability, which is included in accrued wages and benefits in the Consolidated Balance Sheets as of December 31, 2020 and 2019, is as follows: (In thousands) 2020 2019 Balance at beginning of period $ 1,568 $ 185 Plus: Amounts charged to cost and expense 6,229 6,014 Less: Amounts paid (3,611 ) (4,631 ) Balance at end of period $ 4,186 $ 1,568 Restructuring expenses included in the Consolidated Statements of Income (Loss) are for the years ended December 31, 2020, 2019 and 2018: (In thousands) 2020 2019 2018 Cost of sales $ 455 $ 785 $ 2,775 Selling, general and administrative expenses 1,832 2,360 2,655 Research and development expenses 3,942 2,869 1,831 Total restructuring expenses $ 6,229 $ 6,014 $ 7,261 The following table represents the components of restructuring expense by geographic area for the years ended December 31, 2020, 2019 and 2018: (In thousands) 2020 2019 2018 United States $ 2,234 $ 3,336 $ 7,120 International 3,995 2,678 141 Total restructuring expenses $ 6,229 $ 6,014 $ 7,261

Summarized Quarterly Financial

Summarized Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Summarized Quarterly Financial Data (Unaudited)	Note 21 – Summarized Quarterly Financial Data (Unaudited) The following table presents unaudited quarterly operating results for each of the last eight fiscal quarters. This information has been prepared on a basis consistent with the audited financial statements and includes all adjustments, consisting only of normal recurring adjustments, considered necessary for a fair presentation of the data. Unaudited Quarterly Operating Results Three Months Ended (In thousands, except for per share amounts) March 31, 2020 (2) June 30, 2020 September 30, 2020 December 31, 2020 Total Sales $ 114,523 $ 128,715 $ 133,143 $ 130,129 Gross Profit $ 51,600 $ 53,472 $ 58,962 $ 53,517 Operating Income (Loss) $ (4,944 ) $ (6,039 ) $ 4,534 $ (3,324 ) Net Income (Loss) $ (9,969 ) $ 752 $ 5,481 $ 6,114 Earnings (loss) per common share - basic $ (0.21 ) $ 0.02 $ 0.11 $ 0.13 Earnings (loss) per common share - diluted $ (0.21 ) $ 0.02 (1) $ 0.11 (1) $ 0.13 (1) Three Months Ended (In thousands, except for per share amounts) March 31, 2019 June 30, 2019 (2) September 30, 2019 December 31, 2019 Total Sales $ 143,791 $ 156,391 $ 114,092 $ 115,787 Gross Profit $ 60,612 $ 65,015 $ 46,331 $ 47,209 Operating Income (Loss) $ (6,167 ) $ 562 $ (20,288 ) $ (14,070 ) Net Income (Loss) $ 770 $ 3,995 $ (46,123 ) $ (11,624 ) Earnings (loss) per common share - basic $ 0.02 $ 0.08 $ (0.96 ) $ (0.25 ) Earnings (loss) per common share - diluted $ 0.02 (1) $ 0.08 (1) $ (0.96 ) $ (0.25 ) (1) Assumes exercise of dilutive securities calculated under the treasury stock method. (2) See footnote 1 for discussion on out of period disclosures impacting these quarterly operating results.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	Note 22 – Subsequent Events On February 3, 2021, the Company announced that its Board of Directors declared a quarterly cash dividend of $0.09 per common share to be paid to the Company’s stockholders of record at the close of business on February 18, 2021. The payment date will be March 4, 2021 in the aggregate amount of approximately $4.4 million. As part of our required pledged collateral related to a letter for credit agreement entered into with a bank to guarantee performance obligations under a contract with a certain customer, the Company increased its pledged collateral to $15.0 million as of February 2021. We do not anticipate any additional increases in the collateral value at this time as we have reached the maximum amount of the letter of credit required under our contract with the customer. The collateral under the letter of credit will be released when all obligations under the customer contract have been met.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2020
Valuation And Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	SCHEDULE II VALUATION AND QUALIFYING ACCOUNTS (In thousands) Balance at Beginning of Period Charged to Costs & Expenses Deductions Balance at End of Period Year ended December 31, 2020 Allowance for Doubtful Accounts $ 38 — — $ 38 Inventory Reserve $ 34,162 11,404 6,005 $ 39,561 Warranty Liability $ 8,394 1,538 2,786 $ 7,146 Deferred Tax Asset Valuation Allowance $ 48,616 5,120 7,918 $ 45,818 Year ended December 31, 2019 Allowance for Doubtful Accounts $ 128 38 128 $ 38 Inventory Reserve $ 30,009 5,893 1,740 $ 34,162 Warranty Liability $ 8,623 4,569 4,798 $ 8,394 Deferred Tax Asset Valuation Allowance $ 5,816 43,560 760 $ 48,616 Year ended December 31, 2018 Allowance for Doubtful Accounts $ — 128 — $ 128 Inventory Reserve $ 23,355 7,006 352 $ 30,009 Warranty Liability $ 9,724 7,392 8,493 $ 8,623 Deferred Tax Asset Valuation Allowance $ 6,006 — 190 $ 5,816

Nature of Business (Policies)

Nature of Business (Policies)	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Principles of Consolidation	Principles of Consolidation The accompanying Consolidated Financial Statements have been prepared in accordance with accounting principles generally accepted in the U.S. (“U.S. GAAP”) and include the financial position, results of operations, comprehensive income (loss), changes in equity and cash flows of ADTRAN and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
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, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expenses during the reporting period. Our more significant estimates include excess and obsolete inventory reserves, warranty reserves, customer rebates, determination and accrual of the deferred revenue components of multiple element sales agreements, estimated costs to complete obligations associated with deferred revenues and network installations, estimated income tax provision and income tax contingencies, fair value of stock-based compensation, assessment of goodwill and other intangibles for impairment, estimated lives of intangible assets, estimated pension liability, fair value of investments, evaluation of other-than-temporary declines in the value of investments and our allowance for current expected credit losses. Actual amounts could differ significantly from these estimates. We assessed certain accounting matters that generally require consideration of forecasted financial information in context with the information reasonably available to us and the unknown future impacts of the novel coronavirus (“COVID-19”) as of December 31, 2020 and through the date of this report. The accounting matters assessed included, but were not limited to, the allowance for doubtful accounts, current estimated credit losses, stock-based compensation, excess and obsolete inventory reserves, carrying value of goodwill, intangibles and other long-lived assets, financial assets, valuation allowances for tax assets and revenue recognition. While there was not a material impact to our consolidated financial statements as of and for the year ended December 31, 2020 resulting from these assessments, future conditions related to the magnitude and duration of the COVID-19 pandemic, as well as other factors, could result in material impacts to our consolidated financial statements in future reporting periods.
Correction of Immaterial Misstatement	Correction of Immaterial Misstatement During the three months ended June 30, 2019, the Company determined that there was an immaterial misstatement of its excess and obsolete inventory reserves in its previously issued annual and interim financial statements. The Company corrected this misstatement by recognizing a $0.8 million out-of-period adjustment during the three months ended June 30, 2019, which increased its excess and obsolete inventory reserve and cost of goods sold for the period. For the six and twelve months ended June 30, 2019 and December 31, 2019, respectively, the out-of-period adjustment was a cumulative $0.2 million reduction in its excess and obsolete inventory reserve and cost of goods sold. Management determined that the correction of this misstatement was not material to any of its previously issued financial statements on both a quantitative and qualitative basis. During the first quarter of 2020, it was determined that certain investments held in the Company’s stock for a deferred compensation plan accounted for as a Rabbi trust were incorrectly classified as long-term investments with the fair value of such investments incorrectly marked to market at each period end rather than classified as treasury stock held at historical cost. This plan has been in existence since 2011. The Company corrected this misstatement as an out-of-period adjustment in the three months ended March 31, 2020 and the twelve months ended December 31, 2020, by remeasuring the investment assets to their historical cost basis through the recording of a net investment gain of $1.5 million in the Consolidated Statement of Income (Loss) and then correcting the classification by decreasing the long-term investment balance at its remeasured cost basis of $2.8 million to treasury stock in the Consolidated 2020 Balance Sheet. Management has determined that this misstatement was not material to any of its previously issued financial statements and that correction of the misstatement was not material to the 2020 annual financial results on either a quantitative or qualitative basis.
Cash and Cash Equivalents	Summary of Significant Accounting Policies Cash and Cash Equivalents Cash and cash equivalents represent demand deposits, money market funds and short-term investments classified as available-for-sale with original maturities of three months or less. We maintain depository investments with certain financial institutions. As of December 31, 2020, $56.3 million of our cash and cash equivalents, primarily certain domestic money market funds and foreign depository accounts, were in excess of government provided insured depository limits. Although these depository investments may exceed government insured depository limits, we have evaluated the credit worthiness of these applicable financial institutions and determined the risk of material financial loss due to the exposure of such credit risk to be minimal.
Restricted Cash	Restricted Cash Restricted cash consists of certain collateral which secures the Company’s performance obligation under a contract with a certain customer.
Financial Instruments	Financial Instruments The carrying amounts reported in the Consolidated Balance Sheets for cash and cash equivalents, accounts receivable, and accounts payable approximate fair value due to the immediate or short-term maturity of these financial instruments. The carrying amount reported for bonds payable was $24.6 million, which was its fair value as of December 31, 2019. Investments with contractual maturities beyond one year may be classified as short-term based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. Despite the long-term nature of their stated contractual maturities, we routinely buy and sell these securities and we believe we have the ability to quickly sell them to the remarketing agent, tender agent or issuer at par value plus accrued interest in the event we decide to liquidate our investment in a particular variable rate demand note. All income generated from these investments is recorded as interest income. We have not recorded any losses relating to variable rate demand notes. Long-term investments is comprised of deferred compensation plan assets, corporate bonds, municipal fixed-rate bonds, asset-backed bonds, mortgage/agency-backed bonds, U.S. and foreign government bonds, marketable equity securities and other equity investments. Marketable equity securities are reported at fair value as determined by the most recently traded price of the securities at the balance sheet date, although the securities may not be readily marketable due to the size of the available market. Any changes in fair value are recognized in net investment gain (loss). Realized gains and losses on sales of debt securities are computed under the specific identification method and are included in other income (expense). See Note 6 for additional information.
Accounts Receivable	Accounts Receivable We record accounts receivable at net realizable value. Prior to establishing payment terms for a new customer, we evaluate the credit risk of the customer. Credit limits and payment terms established for new customers are re-evaluated periodically based on customer collection experience and other financial factors. As of December 31, 2020, single customers comprising more than 10% of our total accounts receivable balance included three customers, which accounted for 41.5% of our total accounts receivable. As of December 31, 2019, single customers comprising more than 10% of our total accounts receivable balance included four customers, which accounted for 53.2% of our total accounts receivable. On January 1, 2020, we adopted ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . Accounting Policy Under Topic 326 We regularly review the need for an allowance for credit losses related to our outstanding accounts receivable balances using the historical loss-rate method as well as assessing asset-specific risks. The assessment of asset-specific risks included the evaluation of relevant available information, from internal and external sources, relating to current conditions that may affect a customer’s ability to pay, such as the customer’s current financial condition or credit rating by geographic location, as provided by a third party and/or by customer, if needed, and overall macro-economic conditions in which the customer operates. Based on this assessment, an allowance for credit loss would be recorded if the Company determined that, based on our historical write-offs, which have been immaterial, and such asset specific risks, there was risk in collectability of the full amount of any accounts receivable. Accounting Policy Prior to Adoption of Topic 326 Prior to adoption of Topic 326 on January 1, 2020, we regularly reviewed the need to maintain an allowance for doubtful accounts and considered factors such as the age of accounts receivable balances, the current economic conditions that may affect a customer’s ability to pay, significant one-time events impacting these customers and our historical experience. If the financial condition of a customer deteriorated, resulting in an impairment of their ability to make payments, we may have been required to record an allowance for doubtful accounts.
Inventory	Inventory Inventory is carried at the lower of cost and estimated net realizable value, with cost being determined using the first-in, first-out method. Standard costs for material, labor and manufacturing overhead are used to value inventory and are updated at least quarterly. We establish reserves for estimated excess and obsolete inventory equal to the difference between the cost of the inventory and the estimated net realizable value of the inventory based on estimated reserve percentages, which consider historical usage, known trends, inventory age and market conditions. When we dispose of excess and obsolete inventories, the related disposals are charged against the inventory reserve. See Note 7 for additional information.
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment, which is stated at cost, is depreciated using the straight-line method over the estimated useful lives of the assets. We depreciate building and land improvements from five to 39 years, office machinery and equipment from three to seven years, engineering machinery and equipment from three to seven years, and computer software from three to five years. Expenditures for repairs and maintenance are charged to expense as incurred. Major improvements that materially prolong the lives of the assets are capitalized. Gains and losses on the disposal of property, plant and equipment are recorded in operating income (loss). See Note 8 for additional information.
Intangible Assets	Intangible Assets Purchased intangible assets with finite lives are carried at cost less accumulated amortization. Amortization is recorded over the estimated useful lives of the respective assets, which is two to 14 years .
Impairment of Long-Lived Assets and Intangibles	Impairment of Long-Lived Assets and Intangibles Long-lived assets used in operations and intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable and the undiscounted cash flows estimated to be generated by the asset are less than the asset’s carrying value. An impairment loss would be recognized in the amount by which the recorded value of the asset exceeds the fair value of the asset, measured by the quoted market price of an asset or an estimate based on the best information available in the circumstances. During the years ended December 31, 2020 and December 31, 2019, we recognized an impairment loss of less than $0.1 million and $3.9 million, respectively, related to the abandonment of certain information technology implementation projects for which we had previously capitalized expenses. There were no impairment losses for long-lived assets during the year ended December 31, 2018, or for intangible assets recognized during the years ended December 31, 2020, 2019 or 2018.
Goodwill	Goodwill Goodwill represents the excess purchase price over the fair value of net assets acquired. We evaluate the carrying value of goodwill during the fourth quarter of each year and between annual evaluations if events occur or circumstances change that would more likely than not reduce the fair value of the reporting unit below its carrying amount. We have elected to by-pass a qualitative assessment to determine whether it is more likely than not that the fair value of the reporting unit to which the goodwill is assigned is less than its carrying amount and, in turn, performed a step-1 analysis of goodwill. No impairment charges related to goodwill were recognized during the years ended December 31, 2020, 2019 and 2018.
Liability for Warranty	Liability for Warranty Our products generally include warranties of 90 days to five years for product defects. We accrue for warranty returns at the time of product shipment based on our historical return rate and estimate of the cost to repair or replace the defective products. We engage in extensive product quality programs and processes, including actively monitoring and evaluating the quality of our component suppliers. The increasing complexity of our products will cause warranty incidences, when they arise, to be more costly. Our estimates regarding future warranty obligations may change due to product failure rates, material usage and other rework costs incurred in correcting a product failure. In addition, from time to time, specific warranty accruals may be recorded if unforeseen problems arise. Should our actual experience relative to these factors be worse than our estimates, we will be required to record additional warranty expense. The liability for warranty obligations totaled $7.1 million and $8.4 million as of December 31, 2020 and 2019, respectively. These liabilities are included in accrued expenses and other liabilities in the accompanying Consolidated Balance Sheets. A summary of warranty expense and write-off activity for the years ended December 31, 2020, 2019 and 2018 is as follows: Year Ended December 31, (In thousands) 2020 2019 2018 Balance at beginning of period $ 8,394 $ 8,623 $ 9,724 Plus: Amounts charged to cost and expenses 1,538 4,569 7,392 Less: Deductions (2,786 ) (4,798 ) (8,493 ) Balance at end of period $ 7,146 $ 8,394 $ 8,623
Pension Benefit Plan Obligations	Pension Benefit Plan Obligations We maintain a defined benefit pension plan covering employees in certain foreign countries. Pension benefit plan obligations are based on various assumptions used by our actuaries in calculating these amounts. These assumptions include discount rates, compensation rate increases, expected return on plan assets, retirement rates and mortality rates. Actual results that differ from the assumptions and changes in assumptions could affect future expenses and obligations. Our net pension liability totaled $18.7 million and $15.9 million as of December 31, 2020 and 2019, respectively.
Stock-Based Compensation	Stock-Based Compensation We have two stock incentive plans from which stock options, performance stock units (“PSUs”), restricted stock units (“RSUs”) and restricted stock are available for grant to employees and directors. Costs related to these awards are recognized over their vesting periods. All employee and director stock options granted under our stock option plans have an exercise price equal to the fair market value of the award, as defined in the plan, of the underlying common stock on the grant date. All of our outstanding stock option awards are classified as equity awards and therefore are measured at fair value on their grant date. Stock-based compensation expense recognized for the years ended December 31, 2020, 2019 and 2018 was approximately $6.8 million, $7.0 million and $7.2 million, respectively. As of December 31, 2020, total unrecognized compensation cost related to non-vested stock options, PSUs, RSUs and restricted stock was approximately $16.7 million, which is expected to be recognized over an average remaining recognition period of 2.9 years. See Note 5 for additional information.
Research and Development Costs	Research and Development Costs Research and development costs include compensation for engineers and support personnel, contracted services, depreciation and material costs associated with new product development, enhancement of current products and product cost reductions. We continually evaluate new product opportunities and engage in intensive research and product development efforts. Research and development costs totaled $113.3 million, $126.2 million and $124.5 million for the years ended December 31, 2020, 2019 and 2018, respectively.
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) The following table presents changes in accumulated other comprehensive income (loss), net of tax, by components of accumulated other comprehensive income (loss) for the years ended December 31, 2020 2019 and 2018: (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption (2) Total Balance as of December 31, 2017 $ 2,567 $ (4,286 ) $ (1,576 ) $ — $ (3,295 ) Other comprehensive loss before reclassifications 685 (3,890 ) (4,236 ) — (7,441 ) Amounts reclassified to retained earnings (1) (3,220 ) — — — (3,220 ) Amounts reclassified from accumulated other comprehensive loss (595 ) 135 — — (460 ) Balance as of December 31, 2018 (563 ) (8,041 ) (5,812 ) — (14,416 ) Other comprehensive loss before reclassifications 573 (1,717 ) (1,480 ) — (2,624 ) Amounts reclassified to retained earnings (1) — — — 385 385 Amounts reclassified from accumulated other comprehensive loss (294 ) 532 — — 238 Balance as of December 31, 2019 (284 ) (9,226 ) (7,292 ) 385 (16,417 ) Other comprehensive loss before reclassifications 749 (1,231 ) 4,857 — 4,375 Amounts reclassified from accumulated other comprehensive loss (433 ) 836 — — 403 Balance as of December 31, 2020 $ 32 $ (9,621 ) $ (2,435 ) $ 385 $ (11,639 ) (1) With the adoption of ASU 2016-01, the unrealized gains on our equity investments were reclassified to retained earnings. (2) With the adoption of ASU 2018-02 on January 1, 2019, stranded tax effects related to the Tax Cuts and Jobs Act of 2017 were reclassified to retained earnings. See Note 14 for additional information. The following tables present the details of reclassifications out of accumulated other comprehensive income (loss) for the years ended December 31, 2020, 2019 and 2018: (In thousands) For the year ended December 31, Details about Accumulated Other Comprehensive Income Components 2020 2019 2018 Affected Line Item in the Statement Where Net Income Is Presented Unrealized gains on available-for-sale securities: Net realized gain on sales of securities $ 585 $ 397 $ 804 Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (1,212 ) (771 ) (196 ) (1) Total reclassifications for the period, before tax (627 ) (374 ) 608 Tax benefit 224 136 (148 ) Total reclassifications for the period, net of tax $ (403 ) $ (238 ) $ 460 (1) Included in the computation of net periodic pension cost. See Note 15 for additional information. The following tables present the tax effects related to the change in each component of other comprehensive income (loss) for the years ended December 31, 2020, 2019 and 2018: 2020 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gains (losses) on available-for-sale securities $ 1,012 $ (263 ) $ 749 Reclassification adjustment for amounts related to available-for-sale investments included in net income (585 ) 152 (433 ) Defined benefit plan adjustments (1,784 ) 553 (1,231 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income 1,212 (376 ) 836 Foreign currency translation adjustment 4,857 — 4,857 Total Other Comprehensive Income (Loss) $ 4,712 $ 66 $ 4,778 2019 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gains (losses) on available-for-sale securities $ 774 $ (201 ) $ 573 Reclassification adjustment for amounts related to available-for-sale investments included in net loss (397 ) 103 (294 ) Defined benefit plan adjustments (2,488 ) 771 (1,717 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net loss 771 (239 ) 532 Foreign currency translation adjustment (1,480 ) — (1,480 ) Total Other Comprehensive Income (Loss) $ (2,820 ) $ 434 $ (2,386 ) 2018 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gains (losses) on available-for-sale securities $ 926 $ (241 ) $ 685 Reclassification adjustment for amounts related to available-for-sale investments included in net loss (804 ) 209 (595 ) Reclassification adjustment for amounts reclassed to retained earnings related to the adoption of ASU 2016-01 (4,351 ) 1,131 (3,220 ) Defined benefit plan adjustments (5,638 ) 1,748 (3,890 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net loss 196 (61 ) 135 Foreign currency translation adjustment (4,236 ) — (4,236 ) Total Other Comprehensive Income (Loss) $ (13,907 ) $ 2,786 $ (11,121 )
Income Taxes	Income Taxes The provision for income taxes has been determined using the asset and liability approach of accounting for income taxes. Under this approach, deferred taxes represent the future tax consequences expected to occur when the reported amounts of assets and liabilities are recovered or paid. The provision for income taxes represents income taxes paid or payable for the current year plus the change in deferred taxes during the year. Deferred taxes result from the difference between financial and tax bases of our assets and liabilities and are adjusted for changes in tax rates and tax laws when such changes are enacted. Valuation allowances are recorded to reduce deferred tax assets when it is more likely than not that a tax benefit will not be realized. We establish reserves to remove some or all of the tax benefit of any of our tax positions at the time we determine that the positions become uncertain. We adjust these reserves, including any impact on the related interest and penalties, as facts and circumstances change.
Foreign Currency	Foreign Currency Transactions with customers that are denominated in foreign currencies are recorded using the appropriate exchange rates from throughout the year. Assets and liabilities denominated in foreign currencies are remeasured at the balance sheet dates using the closing rates of exchange between those foreign currencies and the functional currency with any transaction gains or losses reported in other income (expense). Our primary exposures to foreign currency exchange rate movements are with our German subsidiary, whose functional currency is the Euro, our Australian subsidiary, whose functional currency is the Australian dollar and our British subsidiary, whose functional currency is the Great British pound. Adjustments resulting from translating financial statements of international subsidiaries are recorded as a component of accumulated other comprehensive income (loss).
Revenue	Revenue On January 1, 2018, we adopted ASU 2014-09, Revenue from Contracts with Customers (Topic 606), Revenue Recognition. Accounting Policy under Topic 606 Revenue is measured based on the consideration expected to be received in exchange for transferring goods or providing services to a customer and as performance obligations under the terms of the contract are satisfied. Generally, this occurs with the transfer of control of a product to the customer. Review of contracts with customers, for both direct customers and distributors, are performed and assessment made regarding principal versus agent considerations to determine primary responsibility for delivery of performance obligation, presumed inventory risk, and discretion in establishing pricing, when applicable. For transactions where there are multiple performance obligations, individual products and services are accounted for separately if they are distinct (if a product or service is separately identifiable from other items and if a customer can benefit from it on its own or with other resources that are readily available to the customer). The consideration, including any discounts, is allocated between separate products and services based on their stand-alone selling prices. Stand-alone selling prices are determined based on the prices at which the separate products and services are sold and are allocated based on each item’s relative value to the total value of the products and services in the arrangement. For items that are not sold separately, we estimate stand-alone selling prices primarily using the “expected cost plus a margin” approach. Payment terms are generally 30 days in the U.S. and typically longer in many geographic markets outside the U.S. Revenue is generated by two reportable segments: Network Solutions and Services & Support. Network Solutions Segment - Includes hardware products and software defined next-generation virtualized solutions used in service provider or business networks, as well as prior generation products. The majority of the revenue from this segment is from hardware revenue. Hardware and Software Revenue Revenue from hardware sales is recognized when control is transferred to the customer, which is generally when the products are shipped. Shipping terms are generally FOB shipping point. Revenue from software license sales are recognized at delivery and transfer of control to the customer. Revenue is recorded net of estimated discounts and rebates using historical trends. Customers are typically invoiced when control is transferred and revenue is recognized. Our products generally include assurance-based warranties of 90 days to five years for product defects, which are accrued at the time products are delivered. Services & Support Segment - A complete portfolio of maintenance, network implementation and solutions integration and managed services, which include hosted cloud services and subscription services to complement our Network Solutions segment. Maintenance Revenue Our maintenance service periods range from one month to five years. Customers are typically invoiced and pay for maintenance services at the beginning of the maintenance period. We recognize revenue for maintenance services on a straight-line basis over the maintenance period as our customers benefit evenly throughout the contract term and deferred revenues, when applicable, are recorded in current and non-current unearned revenue. Network Implementation Revenue We recognize revenue for network implementation, which primarily consists of engineering, execution and enablement services at a point in time when each performance obligation is complete. If we have recognized revenue but have not billed the customer, the right to consideration is recognized as a contract asset that is included in other receivables on the Consolidated Balance Sheet. The contract asset is transferred to accounts receivable when the completed performance obligation is invoiced to the customer. See Notes 4 and 16 for additional information on reportable segments.
Unearned Revenue	Unearned Revenue Unearned revenue primarily represents customer billings on maintenance service programs and unearned revenues related to multiple element contracts where we still have contractual obligations to our customers. We currently offer maintenance contracts ranging from one month to five years. Revenue attributable to maintenance contracts is recognized on a straight-line basis over the related contract term. In addition, we provide software maintenance and a variety of hardware maintenance services to customers under contracts with terms up to ten years. When we defer revenue related to multiple performance obligations where we still have contractual obligations, we also defer the related costs. Current deferred costs are included in prepaid expenses and other current assets on the accompanying Consolidated Balance Sheets and totaled $1.1 million and $1.6 million as of December 31, 2020 and 2019, respectively. Non-current deferred costs are included in other non-current assets on the accompanying Consolidated Balance Sheets and totaled less than $0.1 million and $0.1 million as of December 31, 2020 and 2019, respectively.
Earnings (Loss) per Share	Earnings (Loss) per Share Earnings (loss) per common share and earnings (loss) per common share assuming dilution, are based on the weighted average number of common shares and, when dilutive, common equivalent shares outstanding during the year. See Note 19 for additional information.
Business Combinations	Business Combinations The Company records assets acquired, liabilities assumed, contractual contingencies, when applicable, and intangible assets recognized as part of business combinations based on their fair values on the date of acquisition. The excess of the purchase price over the estimated fair values of the net tangible and intangible assets and liabilities assumed or acquired is recorded as goodwill. If the estimated fair values of net tangible and intangible assets acquired and liabilities assumed exceed the purchase price, a bargain purchase gain is recorded. The Company’s estimates of fair value are based on historical experience, industry knowledge, certain information obtained from the management of the acquired company and, in some cases, valuations performed by independent third-party firms. The results of operations of acquired companies are included in the accompanying Consolidated Statements of Income (Loss) since their dates of acquisition. Costs incurred to complete the business combination, such as legal, accounting or other professional fees are charged to selling, general and administrative expenses as incurred.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2018, the Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2 Compensation – Retirement Benefits – Defined Benefit Plans – General (Subtopic 715-20): Disclosure Framework – Changes to the Disclosure Requirements for Defined Benefit Plans, In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, Fair Value Measurement. Concepts Statement No. 8 — Conceptual Framework for Financial Reporting — Chapter 8 — Notes to Financial Statements In August 2018, the FASB issued ASU 2018-15, Intangibles – Goodwill and Other – Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement. The following table illustrates the impact of adoption of ASU 2018-15 on the Consolidated Balance Sheet as of December 31, 2019: As of December 31, 2019 (In thousands) Pre-Adoption Effect of Adoption As Presented Now Consolidated Balance Sheet Property, plant and equipment, net $ 73,708 $ (5,622 ) $ 68,086 Other non-current assets $ 14,261 $ 5,622 $ 19,883 There was no impact upon adoption of ASU 2018-15 on the Consolidated Statement of Income (Loss) for the year ended December 31, 2019 and the Consolidated Statement of Cash Flows for the year ended December 31, 2019 as outlined in the following tables: For the year ended December 31, 2019 (In thousands) Pre-Adoption Effect of Adoption As Presented Now Consolidated Statement of Income (Loss) Net income (loss) $ (52,982 ) $ — $ (52,982 ) Consolidated Statement of Cash Flows Net cash provided by (used in) operating activities $ (2,472 ) $ — $ (2,472 ) The following table presents the capitalized implementation costs incurred with hosting arrangements, included in other non-current assets on the Consolidated Balance Sheet, as of December 31, 2020: (In thousands) December 31, 2020 Implementation costs - hosting arrangements $ 13,515 Less: accumulated amortization — Implementation costs - hosting arrangements, net $ 13,515 In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. Codification Improvements to Topic 326 Financial Instruments – Credit Losses, Codification Improvements to Topic 326, Financial Instruments–Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments, Financial Instruments – Credit Losses (Topic 326): Targeted Transition Relief, Codification Improvements to Topic 326, Financial Instruments – Credit Losses Codification Improvements to financial instruments, Transfers and Servicing – Sales of Financial Assets. elected to carry forward legacy disclosures for comparative periods and did not adjust the comparative period financial information. Additionally, the Company made an accounting policy election, at the class of financing receivable, not to measure the allowance for credit losses for accrued interest receivables, as the Company writes off the uncollectable accrued interest receivable by reversing any previously recorded interest income in a timely manner (as soon as these amounts are determined to be uncollectable). The adoption of this standard did not have a material effect on our consolidated financial statements. See Note 18 for additional information. In January 2017, the FASB issued ASU 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment The Company adopted ASU 2017-04 on January 1, 2020 , and the amendments were applied prospectively. The adoption of this standard did not have a material effect on our consolidated financial statements.

Nature of Business (Tables)

Nature of Business (Tables)	12 Months Ended
	Dec. 31, 2020
Summary of Warranty Expense and Write-Off Activity	A summary of warranty expense and write-off activity for the years ended December 31, 2020, 2019 and 2018 is as follows: Year Ended December 31, (In thousands) 2020 2019 2018 Balance at beginning of period $ 8,394 $ 8,623 $ 9,724 Plus: Amounts charged to cost and expenses 1,538 4,569 7,392 Less: Deductions (2,786 ) (4,798 ) (8,493 ) Balance at end of period $ 7,146 $ 8,394 $ 8,623
Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax by Components of Accumulated Other Comprehensive Income (Loss)	The following table presents changes in accumulated other comprehensive income (loss), net of tax, by components of accumulated other comprehensive income (loss) for the years ended December 31, 2020 2019 and 2018: (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption (2) Total Balance as of December 31, 2017 $ 2,567 $ (4,286 ) $ (1,576 ) $ — $ (3,295 ) Other comprehensive loss before reclassifications 685 (3,890 ) (4,236 ) — (7,441 ) Amounts reclassified to retained earnings (1) (3,220 ) — — — (3,220 ) Amounts reclassified from accumulated other comprehensive loss (595 ) 135 — — (460 ) Balance as of December 31, 2018 (563 ) (8,041 ) (5,812 ) — (14,416 ) Other comprehensive loss before reclassifications 573 (1,717 ) (1,480 ) — (2,624 ) Amounts reclassified to retained earnings (1) — — — 385 385 Amounts reclassified from accumulated other comprehensive loss (294 ) 532 — — 238 Balance as of December 31, 2019 (284 ) (9,226 ) (7,292 ) 385 (16,417 ) Other comprehensive loss before reclassifications 749 (1,231 ) 4,857 — 4,375 Amounts reclassified from accumulated other comprehensive loss (433 ) 836 — — 403 Balance as of December 31, 2020 $ 32 $ (9,621 ) $ (2,435 ) $ 385 $ (11,639 ) (1) With the adoption of ASU 2016-01, the unrealized gains on our equity investments were reclassified to retained earnings. (2) With the adoption of ASU 2018-02 on January 1, 2019, stranded tax effects related to the Tax Cuts and Jobs Act of 2017 were reclassified to retained earnings. See Note 14 for additional information.
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)	The following tables present the details of reclassifications out of accumulated other comprehensive income (loss) for the years ended December 31, 2020, 2019 and 2018: (In thousands) For the year ended December 31, Details about Accumulated Other Comprehensive Income Components 2020 2019 2018 Affected Line Item in the Statement Where Net Income Is Presented Unrealized gains on available-for-sale securities: Net realized gain on sales of securities $ 585 $ 397 $ 804 Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (1,212 ) (771 ) (196 ) (1) Total reclassifications for the period, before tax (627 ) (374 ) 608 Tax benefit 224 136 (148 ) Total reclassifications for the period, net of tax $ (403 ) $ (238 ) $ 460 (1) Included in the computation of net periodic pension cost. See Note 15 for additional information.
Tax Effects Related to the Change in Each Component of Other Comprehensive Income (Loss)	The following tables present the tax effects related to the change in each component of other comprehensive income (loss) for the years ended December 31, 2020, 2019 and 2018: 2020 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gains (losses) on available-for-sale securities $ 1,012 $ (263 ) $ 749 Reclassification adjustment for amounts related to available-for-sale investments included in net income (585 ) 152 (433 ) Defined benefit plan adjustments (1,784 ) 553 (1,231 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income 1,212 (376 ) 836 Foreign currency translation adjustment 4,857 — 4,857 Total Other Comprehensive Income (Loss) $ 4,712 $ 66 $ 4,778 2019 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gains (losses) on available-for-sale securities $ 774 $ (201 ) $ 573 Reclassification adjustment for amounts related to available-for-sale investments included in net loss (397 ) 103 (294 ) Defined benefit plan adjustments (2,488 ) 771 (1,717 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net loss 771 (239 ) 532 Foreign currency translation adjustment (1,480 ) — (1,480 ) Total Other Comprehensive Income (Loss) $ (2,820 ) $ 434 $ (2,386 ) 2018 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gains (losses) on available-for-sale securities $ 926 $ (241 ) $ 685 Reclassification adjustment for amounts related to available-for-sale investments included in net loss (804 ) 209 (595 ) Reclassification adjustment for amounts reclassed to retained earnings related to the adoption of ASU 2016-01 (4,351 ) 1,131 (3,220 ) Defined benefit plan adjustments (5,638 ) 1,748 (3,890 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net loss 196 (61 ) 135 Foreign currency translation adjustment (4,236 ) — (4,236 ) Total Other Comprehensive Income (Loss) $ (13,907 ) $ 2,786 $ (11,121 )
Schedule of Capitalized Implementation Costs Incurred with Hosting Arrangements, Included in Other Assets on Consolidated Balance Sheet	The following table presents the capitalized implementation costs incurred with hosting arrangements, included in other non-current assets on the Consolidated Balance Sheet, as of December 31, 2020: (In thousands) December 31, 2020 Implementation costs - hosting arrangements $ 13,515 Less: accumulated amortization — Implementation costs - hosting arrangements, net $ 13,515
ASU 2018-15 [Member]
Schedule of Impact of Adoption of ASU 2018-15 on Condensed Consolidated Balance Sheet, Statement of Income (Loss) and Cash Flows	The following table illustrates the impact of adoption of ASU 2018-15 on the Consolidated Balance Sheet as of December 31, 2019: As of December 31, 2019 (In thousands) Pre-Adoption Effect of Adoption As Presented Now Consolidated Balance Sheet Property, plant and equipment, net $ 73,708 $ (5,622 ) $ 68,086 Other non-current assets $ 14,261 $ 5,622 $ 19,883 There was no impact upon adoption of ASU 2018-15 on the Consolidated Statement of Income (Loss) for the year ended December 31, 2019 and the Consolidated Statement of Cash Flows for the year ended December 31, 2019 as outlined in the following tables: For the year ended December 31, 2019 (In thousands) Pre-Adoption Effect of Adoption As Presented Now Consolidated Statement of Income (Loss) Net income (loss) $ (52,982 ) $ — $ (52,982 ) Consolidated Statement of Cash Flows Net cash provided by (used in) operating activities $ (2,472 ) $ — $ (2,472 )

Cash, Cash Equivalents and Re_2

Cash, Cash Equivalents and Restricted Cash (Tables)	12 Months Ended
	Dec. 31, 2020
Cash And Cash Equivalents [Abstract]
Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Consolidated Balance Sheet that sum to the total of the same such amounts shown in the Consolidated Statement of Cash Flows: (In thousands) December 31, 2020 Cash and cash equivalents $ 60,161 Restricted cash 18 Cash, cash equivalents and restricted cash $ 60,179

Business Combinations (Tables)

Business Combinations (Tables)	12 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
Summary of Actual Revenue and Net Loss Included in Consolidated Statements of Income	The Consolidated Statement of Income for the year ended December 31, 2018 includes the following revenue and net loss attributable to SmartRG and Sumitomo since the date of acquisition: (In thousands) March 19, 2018 to December 31, 2018 Revenue $ 9,186 Net loss $ (1,297 )
Summary of Unaudited Supplemental Pro Forma Information	The following unaudited supplemental pro forma information presents the financial results as if the acquisition of SmartRG and Sumitomo had occurred on January 1, 2017. This unaudited supplemental pro forma information does not purport to be indicative of what would have occurred had the acquisition been completed on January 1, 2018, nor is it indicative of any future results. There were no material, non-recurring adjustments to this unaudited pro forma information. (In thousands) 2018 Pro forma revenue $ 559,050 Pro forma net loss $ (33,862 )

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Dec. 31, 2020
Revenue From Contract With Customer [Abstract]
Disaggregate of Revenue by Reportable Segment and Revenue Category	The following table disaggregates revenue by reportable segment and revenue category for the year ended December 31, 2020: (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 262,578 $ 50,560 $ 313,138 Subscriber Solutions & Experience 161,824 9,263 171,087 Traditional & Other Products 13,613 8,672 22,285 Total $ 438,015 $ 68,495 $ 506,510 The following table disaggregates revenue by reportable segment and revenue category for the year ended December 31, 2019: (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 289,980 $ 58,894 $ 348,874 Subscriber Solutions & Experience 144,651 8,269 152,920 Traditional & Other Products 20,595 7,672 28,267 Total $ 455,226 $ 74,835 $ 530,061 The following table disaggregates revenue by reportable segment and revenue category for the year ended December 31, 2018: (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 301,801 $ 57,069 $ 358,870 Subscriber Solutions & Experience 129,067 5,393 134,460 Traditional & Other Products 27,364 8,583 35,947 Total $ 458,232 $ 71,045 $ 529,277 The following tables disaggregate our revenue by category for the years ended December 31, 2020, 2019 and 2018: 2020 (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 262,578 $ 50,560 $ 313,138 Subscriber Solutions & Experience 161,824 9,263 171,087 Traditional & Other Products 13,613 8,672 22,285 Total $ 438,015 $ 68,495 $ 506,510 2019 (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 289,980 $ 58,894 $ 348,874 Subscriber Solutions & Experience 144,651 8,269 152,920 Traditional & Other Products 20,595 7,672 28,267 Total $ 455,226 $ 74,835 $ 530,061 2018 (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 301,801 $ 57,069 $ 358,870 Subscriber Solutions & Experience 129,067 5,393 134,460 Traditional & Other Products 27,364 8,583 35,947 Total $ 458,232 $ 71,045 $ 529,277
Information about Receivable, Contract Assets, and Unearned Revenue from Contracts with Customers	The following table provides information about accounts receivable, contract assets and unearned revenue from contracts with customers: (In thousands) December 31, 2020 December 31, 2019 Accounts receivable $ 98,827 $ 90,531 Contract assets (1) $ 63 $ 2,812 Unearned revenue $ 14,092 $ 11,963 Non-current unearned revenue $ 6,888 $ 6,012 (1)

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Stock-Based Compensation Expense Related to Stock Options, PSUs, RSUs and Restricted Stock	The following table summarizes stock-based compensation expense related to stock options, PSUs, RSUs and restricted stock for the years ended December 31, 2020, 2019 and 2018: (In thousands) 2020 2019 2018 Stock-based compensation expense included in cost of sales $ 426 $ 369 $ 418 Selling, general and administrative expenses 4,036 3,889 3,989 Research and development expenses 2,372 2,704 2,748 Stock-based compensation expense included in operating expenses 6,408 6,593 6,737 Total stock-based compensation expense 6,834 6,962 7,155 Tax benefit for expense associated with non-qualified stock options, PSUs, RSUs and restricted stock (1,629 ) (1,659 ) (1,432 ) Total stock-based compensation expense, net of tax $ 5,205 $ 5,303 $ 5,723
Summary of PSUs, RSUs and Restricted Stock Outstanding	The following table is a summary of our PSUs, RSUs and restricted stock outstanding as of December 31, 2019 and 2020 and the changes that occurred during 2020: Number of shares ( In thousands Weighted Average Grant Date Fair Value Unvested PSUs, RSUs and restricted stock outstanding, December 31, 2019 1,891 $ 14.58 PSUs, RSUs and restricted stock granted 1,029 $ 11.02 PSUs, RSUs and restricted stock vested (453 ) $ 14.26 PSUs, RSUs and restricted stock forfeited (621 ) $ 18.14 Unvested PSUs, RSUs and restricted stock outstanding, December 31, 2020 1,846 $ 11.49
Summary of Stock Options Outstanding	The following table is a summary of stock options outstanding as of December 31, 2020 and 2019 and the changes that occurred during 2020: Number of Options ( I Weighted Average Exercise Price (Per share) Weighted Avg. Remaining Contractual Life in Years Aggregate Intrinsic (In thousands) Stock options outstanding, December 31, 2019 3,572 $ 22.88 3.40 $ — Stock options granted — $ — Stock options exercised — $ — Stock options forfeited — $ — Stock options expired (854 ) $ 28.00 Stock options outstanding, December 31, 2020 2,718 $ 21.17 2.86 $ — Stock options exercisable, December 31, 2020 2,718 $ 21.17 2.86 $ —
Stock Options Outstanding	The following table further describes our stock options outstanding as of December 31, 2020: Options Outstanding Options Exercisable Range of Exercise Prices Options Outstanding at December 31, 2020 (In thousands) Weighted Avg. Remaining Contractual Life in Years Weighted Average Exercise Price Options Exercisable at December 31, 2020 (In thousands) Weighted Average Exercise Price $15.33 – $18.96 1,007 3.69 $ 15.91 1,007 $ 15.91 $18.97 – $23.45 588 3.68 $ 18.97 588 $ 18.97 $23.46 – $30.35 603 2.55 $ 24.11 603 $ 24.11 $30.36 – $41.92 520 0.64 $ 30.40 520 $ 30.40 2,718 2,718
Market-Based PSUs [Member]
Summary of Weighted-Average Assumptions and Value of Options Granted	The following table details the significant assumptions that impact the fair value estimate of the market-based PSUs: 2020 2019 2018 Estimated fair value per share $14.43 $9.53 to $18.05 $16.59 Expected volatility 51.88% 32.7% to 38.9% 27.98% to 31.58% Risk-free interest rate 0.24% 1.6% to 2.46% 2.11% to 2.99% Expected dividend yield 2.85% 2.3% to 4.09% 1.83% to 2.49%

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Debt Securities and Other Investments, Included on Consolidated Balance Sheet and Recorded at Fair Value	Debt Securities and Other Investments As of December 31, 2020, the following debt securities and other investments were included in short-term investments and long-term investments on the Consolidated Balance Sheet and recorded at fair value: Amortized Gross Unrealized Fair (In thousands) Cost Gains Losses Value Corporate bonds $ 11,762 $ 123 $ — $ 11,885 Municipal fixed-rate bonds 2,854 30 — 2,884 Asset-backed bonds 6,634 74 — 6,708 Mortgage/Agency-backed bonds 11,536 114 (6 ) 11,644 U.S. government bonds 9,763 112 — 9,875 Foreign government bonds 1,334 4 (1 ) 1,337 Commercial Paper 250 — — 250 Other 533 — — 533 Available-for-sale debt securities held at fair value $ 44,666 $ 457 $ (7 ) $ 45,116 As of December 31, 2019, the following debt securities and other investments were included in short-term investments and long-term investments on the Consolidated Balance Sheet and recorded at fair value: Amortized Gross Unrealized Fair (In thousands) Cost Gains Losses Value Corporate bonds $ 9,304 $ 80 $ — $ 9,384 Municipal fixed-rate bonds 930 — — 930 Asset-backed bonds 6,867 26 (3 ) 6,890 Mortgage/Agency-backed bonds 6,944 26 (8 ) 6,962 U.S. government bonds 12,311 21 (9 ) 12,323 Foreign government bonds 372 — (1 ) 371 Variable rate demand notes 800 — — 800 Available-for-sale debt securities held at fair value $ 37,528 $ 153 $ (21 ) $ 37,660
Contractual Maturities of Debt Securities	As of December 31, 2020, our debt securities had the following contractual maturities: (In thousands) Corporate bonds Municipal fixed-rate bonds Asset-backed bonds Mortgage / Agency-backed bonds U.S. government bonds Foreign government bonds Commercial paper Other Less than one year $ 1,477 $ 96 $ 144 $ 63 $ — $ 75 $ 250 $ 533 One to two years 2,007 1,245 300 2,129 5,122 462 — — Two to three years 7,013 1,246 622 2,940 4,526 498 — — Three to five years 1,388 297 3,658 183 227 302 — — Five to ten years — — 1,241 2,095 — — — — More than ten years — — 743 4,234 — — — — Total $ 11,885 $ 2,884 $ 6,708 $ 11,644 $ 9,875 $ 1,337 $ 250 $ 533
Gross Realized Gains and Losses on Sale of Debt Securities	The following table presents gross realized gains and losses related to our debt securities for the years ended December 31, 2020, 2019 and 2018: For the year ended December 31, (In thousands) 2020 2019 2018 Gross realized gains on debt securities $ 459 $ 108 $ 57 Gross realized losses on debt securities (58 ) (50 ) (592 ) Total gain (loss) recognized, net $ 401 $ 58 $ (535 )
Breakdown of Investments with Unrealized Losses	The following table presents the breakdown of debt securities and other investments with unrealized losses as of December 31, 2020: Continuous Unrealized Loss Position for Less than 12 Months Continuous Unrealized Loss Position for 12 Months or Greater Total (In thousands) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate bonds $ 336 $ — $ — $ — $ 336 $ — Municipal fixed-rate bonds 310 — — — 310 — Asset-backed bonds 2 — — — 2 — Mortgage/Agency-backed bonds 2,078 (6 ) — — 2,078 (6 ) U.S. government bonds 350 — — — 350 — Foreign government bonds 302 (1 ) — — 302 (1 ) Total $ 3,378 $ (7 ) $ — $ — $ 3,378 $ (7 ) The following table presents the breakdown of debt securities and other investments with unrealized losses as of December 31, 2019: Continuous Unrealized Loss Position for Less than 12 Months Continuous Unrealized Loss Position for 12 Months or Greater Total (In thousands) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate bonds $ 203 $ — $ — $ — $ 203 $ — Municipal fixed-rate bonds 930 — — — 930 — Asset-backed bonds 797 (3 ) — — 797 (3 ) Mortgage/Agency-backed bonds 2,594 (6 ) 136 (2 ) 2,730 (8 ) U.S. government bonds 4,070 (9 ) — — 4,070 (9 ) Foreign government bonds 371 (1 ) — — 371 (1 ) Total $ 8,965 $ (19 ) $ 136 $ (2 ) $ 9,101 $ (21 )
Realized and Unrealized Gains and Losses for Marketable Equity Securities	Realized and unrealized gains and losses for our marketable equity securities for the year ended December 31, 2020, 2019 and 2018 were as follows: For the year ended December 31, (In thousands) 2020 2019 2018 Realized losses on equity securities sold $ (2,382 ) $ (96 ) $ 1,306 Unrealized gains on equity securities held 6,831 11,472 (4,821 ) Total gain (loss) recognized, net $ 4,449 $ 11,376 $ (3,515 )
Cash Equivalents and Investments held at Fair Value	The Company’s cash equivalents and investments held at fair value are categorized into this hierarchy as follows: Fair Value Measurements as of December 31, 2020 Using (In thousands) Fair Value Quoted Prices in Active Market for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash equivalents Money market funds $ 497 $ 497 $ — $ — U.S. government bonds 350 350 — — Available-for-sale debt securities Corporate bonds 11,885 — 11,885 — Municipal fixed-rate bonds 2,884 — 2,884 — Asset-backed bonds 6,708 — 6,708 — Mortgage/Agency-backed bonds 11,644 — 11,644 — U.S. government bonds 9,875 9,875 — — Foreign government bonds 1,337 — 1,337 — Commercial paper 250 — 250 — Other investments 533 — — 533 Marketable equity securities Marketable equity securities – various industries 10,963 10,963 — — Deferred compensation plan assets 23,891 23,891 — — Other investments 1,400 1,400 — — Total $ 82,217 $ 46,976 $ 34,708 $ 533 Fair Value Measurements as of December 31, 2019 Using (In thousands) Fair Value Quoted Prices in Active Market for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash equivalents Money market funds $ 1,309 $ 1,309 $ — $ — Available-for-sale debt securities Corporate bonds 9,384 — 9,384 — Municipal fixed-rate bonds 930 — 930 — Asset-backed bonds 6,890 — 6,890 — Mortgage/Agency-backed bonds 6,962 — 6,962 — U.S. government bonds 12,323 12,323 — — Foreign government bonds 371 — 371 — Variable rate demand notes 800 — 800 — Marketable equity securities Marketable equity securities – various industries 35,501 35,501 — — Equity in escrow 298 298 — — Deferred compensation plan assets 21,698 21,698 — — Other investments 2,442 2,442 — — Total $ 98,908 $ 73,571 $ 25,337 $ —

Inventory (Tables)

Inventory (Tables)	12 Months Ended
	Dec. 31, 2020
Inventory Disclosure [Abstract]
Components of Inventory, Net	As of December 31, 2020 and 2019, inventory, net was comprised of the following: (In thousands) 2020 2019 Raw materials $ 47,026 $ 36,987 Work in process 776 1,085 Finished goods 77,655 60,233 Total Inventory, net $ 125,457 $ 98,305

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property, Plant and Equipment, Net	As of December 31, 2020 and 2019, property, plant and equipment, net was comprised of the following: (In thousands) 2020 2019 Land $ 4,575 $ 4,575 Building and land improvements 35,142 34,797 Building 68,169 68,157 Furniture and fixtures 19,965 19,959 Computer hardware and software 70,942 68,777 Engineering and other equipment 132,920 130,430 Total Property, Plant and Equipment 331,713 326,695 Less: accumulated depreciation (269,314 ) (258,609 ) Total Property, Plant and Equipment, net $ 62,399 $ 68,086

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Schedule of Supplemental Balance Sheet Information Related to Operating Leases	Supplemental balance sheet information related to operating leases is as follows: December 31, December 31, (In thousands) Classification 2020 2019 Assets Operating lease assets Other non-current assets $ 5,309 $ 8,452 Total lease asset $ 5,309 $ 8,452 Liabilities Current operating lease liability Accrued expenses and other liabilities $ 1,806 $ 2,676 Non-current operating lease liability Other non-current liabilities 3,574 5,818 Total lease liability $ 5,380 $ 8,494
Components of Lease Expense included in Consolidated Statement of Income (Loss)	The components of lease expense included in the Consolidated Statements of Income (Loss) were as follows: For the year ended December 31, (In thousands) 2020 2019 Cost of sales $ 113 $ 64 Selling, general and administrative expenses 1,311 1,400 Research and development expenses 1,121 2,417 Total operating lease expense $ 2,545 $ 3,881
Schedule of Maturity of Operating Lease Liabilities	As of December 31, 2020, operating lease liabilities included on the Consolidated Balance Sheet by future maturity were as follows: (In thousands) Amount 2021 $ 1,895 2022 1,600 2023 1,251 2024 521 2025 287 Thereafter — Total lease payments 5,554 Less: Interest (174 ) Present value of lease liabilities $ 5,380
Schedule of Weighted Average Remaining Lease Terms and Weighted Average Discount Rates	The following table provides information about our weighted average lease terms and weighted average discount rates: As of December 31, Weighted average remaining lease term (years) 2020 2019 Operating leases with USD functional currency 2.4 2.6 Operating leases with Euro functional currency 3.6 4.4 Weighted average discount rate Operating leases with USD functional currency 4.47 % 4.02 % Operating leases with Euro functional currency 1.37 % 1.84 %
Schedule of Supplemental Cash Flow Information Related to Operating Leases	Supplemental cash flow information related to operating leases is as follows: As of December 31, (In thousands) 2020 2019 Cash paid for amounts included in the measurement of operating lease assets/liabilities Cash used in operating activities related to operating leases $ 2,632 $ 3,439 Right-of-use assets obtained in exchange for operating lease obligations $ 324 $ 11,615
Components of Net Investment in Sales-Type Leases	As of December 31, 2020 and 2019, the components of the net investment in sales-type leases were as follows: As of December 31, (In thousands) 2020 2019 Current minimum lease payments receivable (1) $ 702 $ 1,201 Non-current minimum lease payments receivable (2) 347 889 Total minimum lease payments receivable 1,049 2,090 Less: Current unearned revenue (1) 218 365 Less: Non-current unearned revenue (2) 50 163 Net investment in sales-type leases $ 781 $ 1,562 (1) Included in other receivables on the Consolidated Balance Sheets. (2) Included in other non-current assets on the Consolidated Balance Sheets.
Schedule of Components of Gross Profit Related to Sales-type Lease and Interest and Dividend Income Included in Consolidated Statements of Income (Loss)	Components of gross profit related to sales-type lease recognized at the lease commencement date and interest and dividend income, included in the Consolidated Statements of Income (Loss) for the year ended December 31, 2020 and 2019 were as follows: For the year ended December 31, (In thousands) 2020 2019 Revenue - Network Solutions $ 78 $ 1,723 Cost of sales - Network Solutions 32 675 Gross profit $ 46 $ 1,048 Interest and dividend income $ 42 $ 357
Schedule of Future Minimum Lease Payments to be Received from Sales-Type Leases	As of December 31, 2020 future minimum lease payments to be received from sales-type leases were as follows: (In thousands) Amount 2021 $ 703 2022 250 2023 88 2024 7 2025 1 Total $ 1,049

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Intangible Assets Net Excluding Goodwill [Abstract]
Summary of Intangible Assets	Intangible assets as of December 31, 2020 and 2019, consisted of the following: 2020 2019 (In thousands) Gross Value Accumulated Amortization Net Value Gross Value Accumulated Amortization Net Value Customer relationships $ 21,123 $ (8,055 ) $ 13,068 $ 22,356 $ (7,233 ) $ 15,123 Developed technology 8,200 (2,546 ) 5,654 10,170 (3,379 ) 6,791 Licensed technology 5,900 (1,830 ) 4,070 5,900 (1,174 ) 4,726 Supplier relationships 2,800 (2,800 ) — 2,800 (2,508 ) 292 Licensing agreements 560 (152 ) 408 560 (79 ) 481 Patents 500 (294 ) 206 500 (226 ) 274 Trade names 210 (146 ) 64 310 (176 ) 134 Total $ 39,293 $ (15,823 ) $ 23,470 $ 42,596 $ (14,775 ) $ 27,821
Estimated Future Amortization Expense Related to Intangible Assets	As of December 31, 2020, estimated future amortization expense of intangible assets was as follows: (In thousands) Amount 2021 $ 4,119 2022 3,494 2023 3,340 2024 3,245 2025 3,031 Thereafter 6,241 Total $ 23,470

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Summary of Components of Income Tax Expense (Benefit)	The components of income tax expense (benefit) for the years ended December 31, 2020, 2019 and 2018 are as follows: (In thousands) 2020 2019 2018 Current Federal $ (10,574 ) $ (518 ) $ (8,001 ) State (329 ) (1,065 ) (476 ) International 3,635 (282 ) 11,705 Total Current (7,268 ) (1,865 ) 3,228 Deferred Federal — 24,801 (14,448 ) State — 5,815 (3,390 ) International (1,356 ) (546 ) 581 Total Deferred (1,356 ) 30,070 (17,257 ) Total Income Tax Expense (Benefit) $ (8,624 ) $ 28,205 $ (14,029 )
Effective Income Tax Rate Differs from Federal Statutory Rate	The effective income tax rate differs from the federal statutory rate due to the following: 2020 2019 2018 Tax provision computed at the federal statutory rate 21.00 % 21.00 % 21.00 % State income tax provision, net of federal benefit 11.10 6.97 14.53 Federal research credits 57.63 15.53 14.23 Foreign taxes (17.83 ) 2.83 (11.45 ) Tax-exempt income 1.93 0.49 0.45 State tax incentives — 3.85 3.15 Change in valuation allowance 44.79 (172.82 ) — Foreign tax credits 17.90 16.69 — Stock-based compensation (23.36 ) (6.01 ) (2.87 ) Withholding taxes (20.83 ) — — Bargain purchase — — 8.82 Impact of CARES Act 45.65 — — Impact of U.S. tax reform — — 12.00 Global intangible low-taxed income ("GILTI") (0.49 ) (1.87 ) (17.48 ) Other, net 0.56 (0.49 ) (0.34 ) Effective Tax Rate 138.05 % (113.83 )% 42.04 %
Income (Loss) Before Expense (Benefit) for Income Taxes	Income (loss) before expense (benefit) for income taxes for the years ended December 31, 2020, 2019 and 2018 is as follows: (In thousands) 2020 2019 2018 U.S. entities $ (12,833 ) $ (29,829 ) $ (74,131 ) International entities 6,587 5,052 40,760 Total $ (6,246 ) $ (24,777 ) $ (33,371 )
Summary of Supplemental Balance Sheet Information Related to Deferred Tax Assets	Deferred income taxes on the Consolidated Balance Sheets result from temporary differences between the amount of assets and liabilities recognized for financial reporting and tax purposes. The significant components of current and non-current deferred taxes as of December 31, 2020 and 2019 consist of the following: (In thousands) 2020 2019 Deferred tax assets: Inventory $ 8,882 $ 7,144 Accrued expenses 2,331 2,330 Deferred compensation 6,714 5,660 Stock-based compensation 1,971 2,451 Uncertain tax positions related to state taxes and related interest 149 241 Pensions 8,554 7,074 Foreign losses 2,590 2,925 State losses and credit carry-forwards 5,509 3,995 Federal loss and research carry-forwards 17,323 12,171 Lease liabilities 1,588 2,496 Capitalized research and development expenditures 11,832 22,230 Valuation allowance (45,818 ) (48,616 ) Total Deferred Tax Assets 21,625 20,101 Deferred tax liabilities: Property, plant and equipment (4,546 ) (2,815 ) Intellectual property (4,375 ) (5,337 ) Right of use lease assets (1,585 ) (2,496 ) Investments (1,250 ) (1,892 ) Total Deferred Tax Liabilities (11,756 ) (12,540 ) Net Deferred Tax Assets $ 9,869 $ 7,561 Supplemental balance sheet information related to deferred tax assets as of December 31, 2020 and 2019 is as follows: December 31, 2020 (In thousands) Deferred Tax Assets Valuation Allowance Deferred Tax Assets, net Domestic $ 43,791 $ (43,791 ) $ — International 11,896 (2,027 ) 9,869 Total $ 55,687 $ (45,818 ) $ 9,869 December 31, 2019 (In thousands) Deferred Tax Assets Valuation Allowance Deferred Tax Assets, net Domestic $ 46,266 $ (46,266 ) $ — International 9,911 (2,350 ) 7,561 Total $ 56,177 $ (48,616 ) $ 7,561
Change in Unrecognized Income Tax Benefits	The change in the unrecognized income tax benefits for the years ended December 31, 2020, 2019 and 2018 is reconciled below: (In thousands) 2020 2019 2018 Balance at beginning of period $ 1,487 $ 1,868 $ 2,366 Increases for tax position related to: Prior years 4 — 3 Current year 165 161 254 Decreases for tax positions related to: Prior years — (71 ) — Expiration of applicable statute of limitations (578 ) (471 ) (755 ) Balance at end of period $ 1,078 $ 1,487 $ 1,868

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Schedule of Pension Benefit Plan Obligations and Funded Status	The pension benefit plan obligations and funded status as of December 31, 2020 and 2019, were as follows: (In thousands) 2020 2019 Change in projected benefit obligation: Projected benefit obligation at beginning of period $ 43,902 $ 37,245 Service cost 1,270 1,471 Interest cost 444 634 Actuarial (gain) loss - experience (744 ) 453 Actuarial loss - assumptions 2,458 5,091 Benefit payments (509 ) (166 ) Effects of foreign currency exchange rate changes 4,106 (826 ) Projected benefit obligation at end of period 50,927 43,902 Change in plan assets: Fair value of plan assets at beginning of period 28,016 24,159 Actual gain on plan assets 1,744 4,392 Contributions 24 — Effects of foreign currency exchange rate changes 2,479 (535 ) Fair value of plan assets at end of period 32,263 28,016 Unfunded status at end of period $ (18,664 ) $ (15,886 )
Summary of Net Amounts Recognized in Consolidated Balance Sheets for the Unfunded Pension Liability	The net amounts recognized in the Consolidated Balance Sheets for the unfunded pension liability as of December 31, 2020 and 2019 were as follows: (In thousands) 2020 2019 Current liability $ — $ — Pension liability 18,664 15,886 Total $ 18,664 $ 15,886
Components of Net Periodic Pension Cost and Amounts Recognized Other Comprehensive Income (Loss)	The components of net periodic pension cost, other than the service cost component, are included in other income (expense), net in the Consolidated Statements of Income (Loss). The components of net periodic pension cost and amounts recognized in other comprehensive income (loss) for the years ended December 31, 2020, 2019 and 2018 were as follows: (In thousands) 2020 2019 2018 Net periodic benefit cost: Service cost $ 1,270 $ 1,471 $ 1,193 Interest cost 444 634 727 Expected return on plan assets (1,679 ) (1,392 ) (1,548 ) Amortization of actuarial losses 970 795 247 Net periodic benefit cost 1,005 1,508 619 Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss): Net actuarial (gain) loss 1,784 2,488 5,638 Amortization of actuarial losses (1,212 ) (771 ) (196 ) Amount recognized in other comprehensive income (loss) 572 1,717 5,442 Total recognized in net periodic benefit cost and other comprehensive income (loss) $ 1,577 $ 3,225 $ 6,061
Accumulated Other Comprehensive Income (Loss)	The amounts recognized in accumulated other comprehensive income (loss) as of December 31, 2020 and 2019 were as follows: (In thousands) 2020 2019 Net actuarial loss $ (13,545 ) $ (12,973 )
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost	The weighted-average assumptions that were used to determine the net periodic benefit cost for the years ended December 31, 2020, 2019 and 2018 were as follows: 2020 2019 2018 Discount rate 1.00 % 1.75 % 2.13 % Rate of compensation increase 2.00 % 2.00 % 2.00 % Expected long-term rates of return 5.90 % 5.90 % 5.90 %
Weighted-Average Assumptions Used to Determine Benefit Obligation	The weighted-average assumptions that were used to determine the benefit obligation as of December 31, 2020 and 2019: 2020 2019 Discount rate 0.69 % 1.00 % Rate of compensation increase 2.00 % 2.00 %
Schedule of Pension Benefit Payments Expected Future Service	The following pension benefit payments, which reflect expected future service, as appropriate, are expected to be paid to participants: (In thousands) 2021 $ 714 2022 1,048 2023 1,348 2024 1,657 2025 1,621 2026 - 2030 7,615 Total $ 14,003
Schedule of Cash Equivalents and Investments Held at Fair Value	We have categorized our cash equivalents and our investments held at fair value into this hierarchy as follows: Fair Value Measurements at December 31, 2020 Using (In thousands) Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents $ 1,935 $ 1,935 $ — $ — Available-for-sale securities Bond funds: Corporate bonds 6,746 6,746 — — Government bonds 5,971 5,971 — — Emerging markets bonds 307 307 — — Equity funds: Global equity 11,638 11,638 — — Balanced fund 2,515 2,515 — — Emerging markets 1,848 1,848 — — Large cap value 198 198 — — Global real estate fund 799 799 — — Managed futures fund 306 306 — — Available-for-sale securities 30,328 30,328 — — Total $ 32,263 $ 32,263 $ — $ — Fair Value Measurements at December 31, 2019 Using (In thousands) Fair Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash and cash equivalents $ 691 $ 691 $ — $ — Available-for-sale securities Bond funds: Government bonds 6,645 6,645 — — Corporate bonds 5,514 5,514 — — Emerging markets bonds 531 531 — — Equity funds: Global equity 11,071 11,071 — — Emerging markets 956 956 — — Balanced fund 863 863 — — Large cap value 312 312 — — Global real estate fund 902 902 — — Managed futures fund 531 531 — — Available-for-sale securities 27,325 27,325 — — Total $ 28,016 $ 28,016 $ — $ —
Fair Value of Assets Held by Trust and Amounts Payable to Plan Participants	The fair value of the assets held by the Trust and the amounts payable to the plan participants as of December 31, 2020 and 2019 were as follows: (In thousands) 2020 2019 Fair Value of Plan Assets Long-term investments $ 23,891 $ 21,698 Total Fair Value of Plan Assets $ 23,891 $ 21,698 Amounts Payable to Plan Participants Deferred compensation liability $ 25,866 $ 21,698 Total Amounts Payable to Plan Participants $ 25,866 $ 21,698

Segment Information and Major_2

Segment Information and Major Customers (Tables)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Sales and Gross Profit of Reportable Segments	The following table presents information about revenue and gross profit of our reportable segments for each of the years ended December 31, 2020, 2019 and 2018: 2020 2019 2018 (In thousands) Revenue Gross Profit Revenue Gross Profit Revenue Gross Profit Network Solutions $ 438,015 $ 193,789 $ 455,226 $ 191,549 $ 458,232 $ 179,303 Services & Support 68,495 23,762 74,835 27,618 71,045 24,262 Total $ 506,510 $ 217,551 $ 530,061 $ 219,167 $ 529,277 $ 203,565
Disaggregate of Revenue by Reportable Segment and Revenue Category	The following table disaggregates revenue by reportable segment and revenue category for the year ended December 31, 2020: (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 262,578 $ 50,560 $ 313,138 Subscriber Solutions & Experience 161,824 9,263 171,087 Traditional & Other Products 13,613 8,672 22,285 Total $ 438,015 $ 68,495 $ 506,510 The following table disaggregates revenue by reportable segment and revenue category for the year ended December 31, 2019: (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 289,980 $ 58,894 $ 348,874 Subscriber Solutions & Experience 144,651 8,269 152,920 Traditional & Other Products 20,595 7,672 28,267 Total $ 455,226 $ 74,835 $ 530,061 The following table disaggregates revenue by reportable segment and revenue category for the year ended December 31, 2018: (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 301,801 $ 57,069 $ 358,870 Subscriber Solutions & Experience 129,067 5,393 134,460 Traditional & Other Products 27,364 8,583 35,947 Total $ 458,232 $ 71,045 $ 529,277 The following tables disaggregate our revenue by category for the years ended December 31, 2020, 2019 and 2018: 2020 (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 262,578 $ 50,560 $ 313,138 Subscriber Solutions & Experience 161,824 9,263 171,087 Traditional & Other Products 13,613 8,672 22,285 Total $ 438,015 $ 68,495 $ 506,510 2019 (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 289,980 $ 58,894 $ 348,874 Subscriber Solutions & Experience 144,651 8,269 152,920 Traditional & Other Products 20,595 7,672 28,267 Total $ 455,226 $ 74,835 $ 530,061 2018 (In thousands) Network Solutions Services & Support Total Access & Aggregation $ 301,801 $ 57,069 $ 358,870 Subscriber Solutions & Experience 129,067 5,393 134,460 Traditional & Other Products 27,364 8,583 35,947 Total $ 458,232 $ 71,045 $ 529,277
Sales Information by Geographic Area	The following table presents revenue information by geographic area for the years ended December 31, 2020, 2019 and 2018: (In thousands) 2020 2019 2018 United States $ 352,079 $ 300,853 $ 288,843 Germany 74,882 78,062 167,251 Mexico 4,087 90,795 12,186 Other international 75,462 60,351 60,997 Total $ 506,510 $ 530,061 $ 529,277

Current Expected Credit Losses

Current Expected Credit Losses (Tables)	12 Months Ended
	Dec. 31, 2020
Credit Loss [Abstract]
Amortized Cost Basis in Sales-Type Leases based on Payment Activity	The following table presents amortized cost basis in sales-type leases based on payment activity: Sales-Type Leases Amortized Cost Basis by Origination Year (In thousands) 2020 2019 2018 2017 2016 Prior Total Payment performance Performing $ 55 $ 192 $ 354 $ 128 $ 52 $ — $ 781 Non-performing — — — — — — — Total $ 55 $ 192 $ 354 $ 128 $ 52 $ — $ 781

Earnings (Loss) Per Share (Tabl

Earnings (Loss) Per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Summary of Calculations of Basic and Diluted Earnings (Loss) Per Share	The calculations of basic and diluted earnings (loss) per share for the years ended December 31, 2020, 2019 and 2018 are as follows: (In thousands, except for per share amounts) 2020 2019 2018 Numerator Net Income (Loss) $ 2,378 $ (52,982 ) $ (19,342 ) Denominator Weighted average number of shares – basic 47,996 47,836 47,880 Effect of dilutive securities: Stock options — — — PSUs, RSUs and restricted stock 292 — — Weighted average number of shares – diluted 48,288 47,836 47,880 Earnings (loss) per share – basic $ 0.05 $ (1.11 ) $ (0.40 ) Earnings (loss) per share – diluted $ 0.05 $ (1.11 ) $ (0.40 )

Restructuring (Tables)

Restructuring (Tables)	12 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Schedule of Reconciliation of Restructuring Liability	A reconciliation of the beginning and ending restructuring liability, which is included in accrued wages and benefits in the Consolidated Balance Sheets as of December 31, 2020 and 2019, is as follows: (In thousands) 2020 2019 Balance at beginning of period $ 1,568 $ 185 Plus: Amounts charged to cost and expense 6,229 6,014 Less: Amounts paid (3,611 ) (4,631 ) Balance at end of period $ 4,186 $ 1,568
Schedule of Components of Restructuring Expense	Restructuring expenses included in the Consolidated Statements of Income (Loss) are for the years ended December 31, 2020, 2019 and 2018: (In thousands) 2020 2019 2018 Cost of sales $ 455 $ 785 $ 2,775 Selling, general and administrative expenses 1,832 2,360 2,655 Research and development expenses 3,942 2,869 1,831 Total restructuring expenses $ 6,229 $ 6,014 $ 7,261 The following table represents the components of restructuring expense by geographic area for the years ended December 31, 2020, 2019 and 2018: (In thousands) 2020 2019 2018 United States $ 2,234 $ 3,336 $ 7,120 International 3,995 2,678 141 Total restructuring expenses $ 6,229 $ 6,014 $ 7,261

Summarized Quarterly Financia_2

Summarized Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Quarterly Operating Results	The following table presents unaudited quarterly operating results for each of the last eight fiscal quarters. This information has been prepared on a basis consistent with the audited financial statements and includes all adjustments, consisting only of normal recurring adjustments, considered necessary for a fair presentation of the data. Unaudited Quarterly Operating Results Three Months Ended (In thousands, except for per share amounts) March 31, 2020 (2) June 30, 2020 September 30, 2020 December 31, 2020 Total Sales $ 114,523 $ 128,715 $ 133,143 $ 130,129 Gross Profit $ 51,600 $ 53,472 $ 58,962 $ 53,517 Operating Income (Loss) $ (4,944 ) $ (6,039 ) $ 4,534 $ (3,324 ) Net Income (Loss) $ (9,969 ) $ 752 $ 5,481 $ 6,114 Earnings (loss) per common share - basic $ (0.21 ) $ 0.02 $ 0.11 $ 0.13 Earnings (loss) per common share - diluted $ (0.21 ) $ 0.02 (1) $ 0.11 (1) $ 0.13 (1) Three Months Ended (In thousands, except for per share amounts) March 31, 2019 June 30, 2019 (2) September 30, 2019 December 31, 2019 Total Sales $ 143,791 $ 156,391 $ 114,092 $ 115,787 Gross Profit $ 60,612 $ 65,015 $ 46,331 $ 47,209 Operating Income (Loss) $ (6,167 ) $ 562 $ (20,288 ) $ (14,070 ) Net Income (Loss) $ 770 $ 3,995 $ (46,123 ) $ (11,624 ) Earnings (loss) per common share - basic $ 0.02 $ 0.08 $ (0.96 ) $ (0.25 ) Earnings (loss) per common share - diluted $ 0.02 (1) $ 0.08 (1) $ (0.96 ) $ (0.25 ) (1) Assumes exercise of dilutive securities calculated under the treasury stock method. (2) See footnote 1 for discussion on out of period disclosures impacting these quarterly operating results.

Nature of Business - Additional

Nature of Business - Additional Information (Detail)	3 Months Ended		6 Months Ended	12 Months Ended
	Mar. 31, 2020USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Dec. 31, 2020USD ($)CustomerIncentivePlan	Dec. 31, 2019USD ($)Customer	Dec. 31, 2018USD ($)	Jan. 01, 2020USD ($)	Dec. 31, 2017USD ($)
Summary Of Significant Accounting Policy [Line Items]
Cash, uninsured amount				$ 56,300,000
Bonds payable, carrying amount					$ 24,600,000
Bonds payable, fair value					$ 24,600,000
Number of single customer comprising more than 10% of account receivable | Customer				3	4
Asset impairments				$ 65,000	$ 3,872,000	$ 0
Impairment losses of long-lived assets						0
Impairment losses of intangible assets				0	0	0
Impairment charges recognized on goodwill				$ 0	0	0
Period of assurance-based warranty for product defects				90 days to five years
Liability for warranty obligations				$ 7,146,000	8,394,000	8,623,000		$ 9,724,000
Pension liability				$ 18,664,000	15,886,000
Number of stock incentive plans | IncentivePlan				2
Stock-based compensation expense				$ 6,834,000	6,962,000	7,155,000
Total unrecognized compensation cost related to non-vested stock options, PSUs, RSUs and restricted stock				$ 16,700,000
Recognition period of unvested compensation expense				2 years 10 months 24 days
Research and development costs				$ 113,287,000	126,200,000	124,547,000
Effect on adoption of ASU				62,399,000	68,086,000
Effect on adoption of ASU				25,425,000	19,883,000
Tax benefit in other comprehensive income (loss)				$ (66,000)	(434,000)	$ (2,786,000)
ASU 2018-14 [Member]
Summary Of Significant Accounting Policy [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]				true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]				true
ASU 2018-13 [Member]
Summary Of Significant Accounting Policy [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]				true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]				true
Change in Accounting Principle, Accounting Standards Update, Adoption Date				Jan. 1, 2020
ASU 2018-15 [Member]
Summary Of Significant Accounting Policy [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]				true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]				true
Change in Accounting Principle, Accounting Standards Update, Adoption Date				Jan. 1, 2020
Effect on adoption of ASU					68,086,000
Effect on adoption of ASU					19,883,000
ASU 2018-15 [Member] | Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Summary Of Significant Accounting Policy [Line Items]
Effect on adoption of ASU							$ (5,600,000)
Effect on adoption of ASU							$ 5,600,000
ASU 2016-13 [Member]
Summary Of Significant Accounting Policy [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]				true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]				true
Change in Accounting Principle, Accounting Standards Update, Adoption Date				Jan. 1, 2020
ASU 2019-12 [Member]
Summary Of Significant Accounting Policy [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]				true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]				true
Change in Accounting Principle, Accounting Standards Update, Adoption Date				Apr. 1, 2020
Adjustments for New Accounting Principle, Early Adoption [Member]
Summary Of Significant Accounting Policy [Line Items]
Tax benefit in other comprehensive income (loss)				$ (100,000)
ASU 2017-04 [Member]
Summary Of Significant Accounting Policy [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]				true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]				true
Change in Accounting Principle, Accounting Standards Update, Adoption Date				Jan. 1, 2020
Prepaid Expenses and Other Current Assets [Member]
Summary Of Significant Accounting Policy [Line Items]
Current deferred costs related to prepaid and other assets				$ 1,100,000	1,600,000
Other Non-Current Assets [Member]
Summary Of Significant Accounting Policy [Line Items]
Non-current deferred costs related to other non-current assets					$ 100,000
Minimum [Member]
Summary Of Significant Accounting Policy [Line Items]
Amortization, estimated useful lives				2 years
Maintenance service periods				1 month
Maintenance contract period				1 month
Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Amortization, estimated useful lives				14 years
Asset impairments				$ 100,000
Maintenance service periods				5 years
Maintenance contract period				5 years
Maximum [Member] | Other Non-Current Assets [Member]
Summary Of Significant Accounting Policy [Line Items]
Non-current deferred costs related to other non-current assets				$ 100,000
Building and Land Improvements [Member] | Minimum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives				5 years
Building and Land Improvements [Member] | Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives				39 years
Office Machinery and Equipment [Member] | Minimum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives				3 years
Office Machinery and Equipment [Member] | Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives				7 years
Engineering Machinery and Equipment [Member] | Minimum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives				3 years
Engineering Machinery and Equipment [Member] | Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives				7 years
Computer Software [Member] | Minimum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives				3 years
Computer Software [Member] | Maximum [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, estimated useful lives				5 years
Credit Concentration Risk [Member] | Accounts Receivable [Member]
Summary Of Significant Accounting Policy [Line Items]
Percentage of accounts receivable accounted by each customers				41.50%	53.20%
Excess, Obsolete Inventory Reserve and Cost of Goods [Member]
Summary Of Significant Accounting Policy [Line Items]
Amount of revision		$ 800,000	$ 200,000		$ 200,000
Errors in Net Investment Gain [Member]
Summary Of Significant Accounting Policy [Line Items]
Amount of revision	$ 1,500,000			$ 1,500,000
Overstatement Long-term Investment Balance at Remeasured Cost Basis [Member]
Summary Of Significant Accounting Policy [Line Items]
Amount of revision				$ 2,800,000

Nature of Business - Summary of

Nature of Business - Summary of Warranty Expense and Write-Off Activity (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Product Warranties Disclosures [Abstract]
Balance at beginning of period	$ 8,394	$ 8,623	$ 9,724
Plus: Amounts charged to cost and expenses	1,538	4,569	7,392
Less: Deductions	(2,786)	(4,798)	(8,493)
Balance at end of period	$ 7,146	$ 8,394	$ 8,623

Nature of Business - Changes in

Nature of Business - Changes in Accumulated Other Comprehensive Income (Loss), Net of Tax by Components Of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 380,426	$ 446,279	$ 497,911
Other comprehensive income (loss) before reclassifications	4,375	(2,624)	(7,441)
Amounts reclassified to retained earnings		385	(3,220)
Amounts reclassified from accumulated other comprehensive loss	403	238	(460)
Ending Balance	372,944	380,426	446,279
ASU 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	385
Amounts reclassified to retained earnings		385
Ending Balance	385	385
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(284)	(563)	2,567
Other comprehensive income (loss) before reclassifications	749	573	685
Amounts reclassified to retained earnings			(3,220)
Amounts reclassified from accumulated other comprehensive loss	(433)	(294)	(595)
Ending Balance	32	(284)	(563)
Defined Benefit Plan Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(9,226)	(8,041)	(4,286)
Other comprehensive income (loss) before reclassifications	(1,231)	(1,717)	(3,890)
Amounts reclassified from accumulated other comprehensive loss	836	532	135
Ending Balance	(9,621)	(9,226)	(8,041)
Foreign Currency Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(7,292)	(5,812)	(1,576)
Other comprehensive income (loss) before reclassifications	4,857	(1,480)	(4,236)
Ending Balance	(2,435)	(7,292)	(5,812)
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(16,417)	(14,416)	(3,295)
Other comprehensive income (loss) before reclassifications			(7,441)
Ending Balance	$ (11,639)	$ (16,417)	$ (14,416)

Nature of Business - Reclassifi

Nature of Business - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit plan adjustments – actuarial losses									$ 2,458	$ 5,091
Loss Before Income Taxes									(6,246)	(24,777)	$ (33,371)
Tax benefit (expense)									8,624	(28,205)	14,029
Net Income (Loss)	$ 6,114	$ 5,481	$ 752	$ (9,969)	$ (11,624)	$ (46,123)	$ 3,995	$ 770	2,378	(52,982)	(19,342)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit plan adjustments – actuarial losses									(1,212)	(771)	(196)
Loss Before Income Taxes									(627)	(374)	608
Tax benefit (expense)									224	136	(148)
Net Income (Loss)									(403)	(238)	460
Unrealized Gains (Losses) on Available-for-Sale Securities [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Net investment gain (loss)									$ 585	$ 397	$ 804

Nature of Business - Tax Effect

Nature of Business - Tax Effects Related to the Change in Each Component of Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Unrealized gain (loss) on available-for-sale securities, Before-Tax Amount	$ 1,012	$ 774	$ 926
Unrealized gain (loss) on available-for-sale securities, Tax (Expense) Benefit	(263)	(201)	(241)
Unrealized gain (loss) on available-for-sale securities, Net-of-Tax Amount	749	573	685
Reclassification adjustment for amounts related to available-for-sale investments included in net income (loss), Before-Tax Amount	(585)	(397)	(804)
Reclassification adjustment for amounts related to available-for-sale investments included in net income (loss), Tax (Expense) Benefit	152	103	209
Reclassification adjustment for amounts related to available-for-sale investments included in net income (loss), Net-of-Tax Amount	(433)	(294)	(595)
Reclassification adjustment for amounts reclassed to retained earnings related of the adoption of ASU 2016-01, Before-Tax Amount			(4,351)
Reclassification adjustment for amounts reclassed to retained earnings related of the adoption of ASU 2016-01, Tax (Expense) Benefit			1,131
Reclassification adjustment for amounts reclassed to retained earnings related of the adoption of ASU 2016-01, Net-of-Tax Amount			(3,220)
Defined benefit plan adjustments, Before-Tax Amount	(1,784)	(2,488)	(5,638)
Defined benefit plan adjustments, Tax (Expense) Benefit	553	771	1,748
Defined benefit plan adjustments, Net-of-Tax Amount	(1,231)	(1,717)	(3,890)
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income (loss), Before-Tax Amount	1,212	771	196
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income (loss), Tax (Expense) Benefit	(376)	(239)	(61)
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income (loss), Net-of-Tax Amount	836	532	135
Foreign currency translation adjustment, Before-Tax Amount	4,857	(1,480)	(4,236)
Foreign currency translation adjustment, Net-of-Tax Amount	4,857	(1,480)	(4,236)
Total Other Comprehensive Income (Loss), Before-Tax Amount	4,712	(2,820)	(13,907)
Total Other Comprehensive Income (Loss), Tax (Expense) Benefit	66	434	2,786
Other Comprehensive Income (Loss), net of tax	$ 4,778	$ (2,386)	$ (11,121)

Nature of Business - Schedule o

Nature of Business - Schedule of Impact of Adoption of ASU 2018-15 on Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, net	$ 62,399	$ 68,086
Other non-current assets	$ 25,425	19,883
ASU 2018-15 [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, net		68,086
Other non-current assets		19,883
Pre-Adoption [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, net		73,708
Other non-current assets		14,261
Effect of Adoption [Member] | ASU 2018-15 [Member]
Summary Of Significant Accounting Policy [Line Items]
Property, plant and equipment, net		(5,622)
Other non-current assets		$ 5,622

Nature of Business - Schedule_2

Nature of Business - Schedule of Impact of Adoption of ASU 2018-15 on Consolidated Statement of Income (Loss) and Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Summary Of Significant Accounting Policy [Line Items]
Net income (loss)	$ 6,114	$ 5,481	$ 752	$ (9,969)	$ (11,624)	$ (46,123)	$ 3,995	$ 770	$ 2,378	$ (52,982)	$ (19,342)
Net cash provided by (used in) operating activities									$ (16,518)	(2,472)	$ 55,454
ASU 2018-15 [Member]
Summary Of Significant Accounting Policy [Line Items]
Net income (loss)										(52,982)
Net cash provided by (used in) operating activities										(2,472)
Pre-Adoption [Member]
Summary Of Significant Accounting Policy [Line Items]
Net income (loss)										(52,982)
Net cash provided by (used in) operating activities										$ (2,472)

Nature of Business - Schedule_3

Nature of Business - Schedule of Capitalized Implementation Costs Incurred with Hosting Arrangements, Included in Other Assets on Consolidated Balance Sheet (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Hosting Arrangement Service Contract [Abstract]
Implementation costs - hosting arrangements	$ 13,515
Implementation costs - hosting arrangements, net	$ 13,515

Cash, Cash Equivalents and Re_3

Cash, Cash Equivalents and Restricted Cash - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 60,161,000	$ 73,773,000
Restricted cash	18,000	$ 0	$ 0
Cash, cash equivalents and restricted cash	$ 60,179,000

Cash, Cash Equivalents and Re_4

Cash, Cash Equivalents and Restricted Cash - Additional Information (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash And Cash Equivalents [Abstract]
Restricted cash	$ 18,000	$ 0	$ 0

Business Combinations - Additio

Business Combinations - Additional Information (Detail) - USD ($) $ in Thousands	Nov. 30, 2018	Jun. 30, 2019	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Goodwill				$ 7,000	$ 7,000
Gain on contingency					1,230
Bargain purchase gain net of income taxes						$ 11,322
SmartRG Inc [Member]
Business Acquisition [Line Items]
Business acquisition, agreement month and year				2018-11
Business acquisition, description				In November 2018, we acquired SmartRG, Inc., for cash consideration. This transaction was accounted for as a business combination. We recorded goodwill of $3.5 million as a result of this acquisition, which represents the excess of the purchase price over the fair value of net assets acquired and liabilities assumed. The financial results of this acquisition are included in the consolidated financial statements since the date of acquisition. The revenues are included in the Subscriber Solutions & Experience category within the Network Solutions and Services & Support reportable segments.
Goodwill	$ 3,500
Business combination, contingent consideration, liability	1,200
Gain on contingency		$ 1,200
Business combination escrow amount	$ 2,800
Business combination escrow fund released					1,300
Sumitomo [Member]
Business Acquisition [Line Items]
Business acquisition, description				In March 2018, we acquired Sumitomo Electric Lightwave Corp.’s (SEL) North American EPON business and entered into a technology license and OEM supply agreement with Sumitomo Electric Industries, Ltd. (SEI).
Date of acquisition				Mar. 31, 2018
Bargain purchase gain net of income taxes			$ 11,300
Smart RG and Sumitomo [Member]
Business Acquisition [Line Items]
Acquisition and integration related expenses and amortization of acquired intangibles				$ 3,800	$ 5,000	$ 2,900

Business Combinations - Summary

Business Combinations - Summary of Actual Revenue and Net Loss Included in Consolidated Statements of Income (Detail) - Smart RG and Sumitomo [Member] $ in Thousands	9 Months Ended
	Dec. 31, 2018USD ($)
Business Acquisition [Line Items]
Revenue	$ 9,186
Net loss	$ (1,297)

Business Combinations - Summa_2

Business Combinations - Summary of Unaudited Supplemental Pro Forma Information (Detail) - Smart RG and Sumitomo [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Business Acquisition [Line Items]
Pro forma revenue	$ 559,050
Pro forma net loss	$ (33,862)

Revenue - Additional Informatio

Revenue - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020USD ($)Category	Dec. 31, 2019USD ($)
Revenue [Line Items]
Number of categories | Category	3
Remaining performance obligations	$ 0
Recognized revenue	11,000,000	$ 12,700,000
Other Than Maintenance Services [Member]
Revenue [Line Items]
Remaining performance obligations	$ 17,700,000	$ 13,600,000

Revenue - Disaggregate of Reven

Revenue - Disaggregate of Revenue by Reportable Segment and Revenue Category (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Revenue	$ 130,129	$ 133,143	$ 128,715	$ 114,523	$ 115,787	$ 114,092	$ 156,391	$ 143,791	$ 506,510	$ 530,061	$ 529,277
Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue									313,138	348,874	358,870
Subscriber Solutions & Experience [Member]
Disaggregation Of Revenue [Line Items]
Revenue									171,087	152,920	134,460
Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue									22,285	28,267	35,947
Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue									438,015	455,226	458,232
Network Solutions [Member] | Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue									262,578	289,980	301,801
Network Solutions [Member] | Subscriber Solutions & Experience [Member]
Disaggregation Of Revenue [Line Items]
Revenue									161,824	144,651	129,067
Network Solutions [Member] | Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue									13,613	20,595	27,364
Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue									68,495	74,835	71,045
Services & Support [Member] | Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue									50,560	58,894	57,069
Services & Support [Member] | Subscriber Solutions & Experience [Member]
Disaggregation Of Revenue [Line Items]
Revenue									9,263	8,269	5,393
Services & Support [Member] | Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue									$ 8,672	$ 7,672	$ 8,583

Revenue - Additional Informat_2

Revenue - Additional Information (Detail1) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-01-01	Dec. 31, 2020
Revenue [Line Items]
Remaining performance obligations, percentage	61.00%
Remaining performance obligations, period	12 months

Revenue - Information about Rec

Revenue - Information about Receivable, Contract Assets, and Unearned Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Revenue From Contract With Customer [Abstract]
Accounts receivable	$ 98,827	$ 90,500	$ 90,531
Contract assets	63	$ 2,800	2,812
Unearned revenue	14,092		11,963
Non-current unearned revenue	$ 6,888		$ 6,012

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense Related to Stock Options, PSUs, RSUs and Restricted Stock (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,834	$ 6,962	$ 7,155
Tax benefit for expense associated with non-qualified stock options, PSUs, RSUs and restricted stock	(1,629)	(1,659)	(1,432)
Total stock-based compensation expense, net of tax	5,205	5,303	5,723
Stock-based Compensation Expense Included in Cost of Sales [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	426	369	418
Selling, General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	4,036	3,889	3,989
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	2,372	2,704	2,748
Stock-based Compensation Expense Included in Operating Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,408	$ 6,593	$ 6,737

Stock-Based Compensation (Stock

Stock-Based Compensation (Stock Incentive Program Descriptions) - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Jan. 31, 2015
PSUs, RSUs and Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	4 years
2015 Employee Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of additional shares of common stock granted	0
Number of shares of common stock authorized		7,700,000
Multiplier used when issuing PSUs, restricted stock and RSUs		2.5
Vesting period	4 years
Contractual term	10 years
2015 Employee Stock Incentive Plan [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration date of options	2025
2015 Employee Stock Incentive Plan [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration date of options	2026
2010 Directors Stock Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of additional shares of common stock granted	0
Number of shares of common stock authorized	500,000
Contractual term	10 years
Expiration date of options	2019
Previous Stock Incentive Plans [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of additional shares of common stock granted	0
2020 Employee Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock authorized	2,800,000
Multiplier used when issuing PSUs, restricted stock and RSUs	1
Contractual term	10 years
2020 Employee Incentive Plan [Member] | PSUs, RSUs and Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	4 years
2020 Employee Incentive Plan [Member] | Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	4 years
2015 Employee Incentive Plan to 2020 Employee Incentive Plan [Member] | PSUs, RSUs and Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Forfeiture of stock increase in issuance of common stock	2.5
2020 Directors Stock Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock authorized	400,000
Multiplier used when issuing PSUs, restricted stock and RSUs	1
Forfeiture of stock increase in issuance of common stock	1
Contractual term	10 years
2006 Employee Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares of common stock authorized	13,000,000
Vesting period	4 years
Contractual term	10 years
2006 Employee Stock Incentive Plan [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration date of options	2021
2006 Employee Stock Incentive Plan [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expiration date of options	2024

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of PSUs, RSUs and Restricted Stock Outstanding (Detail) shares in Thousands	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Unvested PSUs, RSUs and restricted stock outstanding, beginning balance | shares	1,891
Number of Shares, PSUs, RSUs and restricted stock granted | shares	1,029
Number of Shares, PSUs, RSUs and restricted stock vested | shares	(453)
Number of Shares, PSUs, RSUs and restricted stock forfeited | shares	(621)
Number of Shares, Unvested PSUs, RSUs and restricted stock outstanding, ending balance | shares	1,846
Weighted Average Grant Date Fair Value, Unvested PSUs, RSUs and restricted stock outstanding, Beginning Balance | $ / shares	$ 14.58
Weighted Average Grant Date Fair Value, PSUs, RSUs and restricted stock granted | $ / shares	11.02
Weighted Average Grant Date Fair Value, PSUs, RSUs and restricted stock vested | $ / shares	14.26
Weighted Average Grant Date Fair Value, PSUs, RSUs and restricted stock forfeited | $ / shares	18.14
Weighted Average Grant Date Fair Value, Unvested PSUs, RSUs and restricted stock outstanding, Ending Balance | $ / shares	$ 11.49

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Weighted-Average Assumptions and Value of Options Granted (Detail) - Market-Based PSUs [Member] - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated fair value per share	$ 14.43		$ 16.59
Expected volatility	51.88%
Risk-free interest rate	0.24%
Expected dividend yield	2.85%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated fair value per share		$ 9.53
Expected volatility		32.70%	27.98%
Risk-free interest rate		1.60%	2.11%
Expected dividend yield		2.30%	1.83%
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated fair value per share		$ 18.05
Expected volatility		38.90%	31.58%
Risk-free interest rate		2.46%	2.99%
Expected dividend yield		4.09%	2.49%

Stock-Based Compensation (PSUs,

Stock-Based Compensation (PSUs, RSUs and Restricted Stock) - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Recognition period of non-vested compensation cost		2 years 10 months 24 days
Performance Stock Units (PSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		3 years
Share issued	0.3
Performance target period	3 years
Performance Stock Units (PSUs) [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of performance stock units granted	0.00%	0.00%
Performance Stock Units (PSUs) [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of performance stock units granted	142.80%	150.00%
PSUs, RSUs and Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		4 years
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period		1 year
Market-Based PSUs, RSUs and Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense related to other than options		$ 16.7
Recognition period of non-vested compensation cost		2 years 10 months 24 days
Stock Options, PSUs, RSUs or Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options available for issuance under shareholders-approved equity plan		3.6

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Stock Options Outstanding (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Stock options outstanding, Beginning Balance	3,572,000
Number of Options, Stock options granted	0	0	0
Number of Options, Stock options expired	(854,000)
Number of Options, Stock options outstanding, Ending Balance	2,718,000	3,572,000
Number of Options, Stock options exercisable	2,718,000
Weighted Average Exercise Price, Stock options outstanding, Beginning Balance	$ 22.88
Weighted Average Exercise Price, Stock options expired	28
Weighted Average Exercise Price, Stock options outstanding, Ending Balance	21.17	$ 22.88
Weighted Average Exercise Price, Stock options exercisable	$ 21.17
Weighted Avg. Remaining Contractual Life in Years, Stock options outstanding	2 years 10 months 9 days	3 years 4 months 24 days
Weighted Avg. Remaining Contractual Life in Years, Stock options exercisable	2 years 10 months 9 days
Aggregate Intrinsic Value, Stock options outstanding	$ 0

Stock-Based Compensation (Sto_2

Stock-Based Compensation (Stock Options) - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate intrinsic value based on fair market value	$ 0
Total pre-tax intrinsic value of options exercised	$ 0	$ 100,000	$ 200,000
Fair value of options fully vested		$ 900,000	$ 2,500,000
Number of Stock options, granted	0	0	0
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of options fully vested	$ 100,000
Unvested Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense related to non-vested stock options	$ 0

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock Options Outstanding (Detail) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding at 12/31/20	2,718	3,572
Options Exercisable at 12/31/20	2,718
Weighted Average Exercise Price, Options exercisable	$ 21.17
$15.33 - 18.96 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Lower Range Limit	15.33
Upper Range Limit	$ 18.96
Options Outstanding at 12/31/20	1,007
Weighted Avg. Remaining Contractual Life In Years, Options Outstanding	3 years 8 months 8 days
Weighted Average Exercise Price, Options Outstanding	$ 15.91
Options Exercisable at 12/31/20	1,007
Weighted Average Exercise Price, Options exercisable	$ 15.91
$18.97 - 23.45 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Lower Range Limit	18.97
Upper Range Limit	$ 23.45
Options Outstanding at 12/31/20	588
Weighted Avg. Remaining Contractual Life In Years, Options Outstanding	3 years 8 months 4 days
Weighted Average Exercise Price, Options Outstanding	$ 18.97
Options Exercisable at 12/31/20	588
Weighted Average Exercise Price, Options exercisable	$ 18.97
$23.46 - 30.35 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Lower Range Limit	23.46
Upper Range Limit	$ 30.35
Options Outstanding at 12/31/20	603
Weighted Avg. Remaining Contractual Life In Years, Options Outstanding	2 years 6 months 18 days
Weighted Average Exercise Price, Options Outstanding	$ 24.11
Options Exercisable at 12/31/20	603
Weighted Average Exercise Price, Options exercisable	$ 24.11
$30.36 - 41.92 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Lower Range Limit	30.36
Upper Range Limit	$ 41.92
Options Outstanding at 12/31/20	520
Weighted Avg. Remaining Contractual Life In Years, Options Outstanding	7 months 20 days
Weighted Average Exercise Price, Options Outstanding	$ 30.40
Options Exercisable at 12/31/20	520
Weighted Average Exercise Price, Options exercisable	$ 30.40

Investments - Debt Securities a

Investments - Debt Securities and Other Investments, Included on Consolidated Balance Sheet and Recorded at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 44,666		$ 37,528
Gross Unrealized Gains	457		153
Gross Unrealized Losses	(7)		(21)
Fair Value	45,116	$ 37,700	37,660
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,762		9,304
Gross Unrealized Gains	123		80
Fair Value	11,885		9,384
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,854		930
Gross Unrealized Gains	30
Fair Value	2,884		930
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,634		6,867
Gross Unrealized Gains	74		26
Gross Unrealized Losses			(3)
Fair Value	6,708		6,890
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,536		6,944
Gross Unrealized Gains	114		26
Gross Unrealized Losses	(6)		(8)
Fair Value	11,644		6,962
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,763		12,311
Gross Unrealized Gains	112		21
Gross Unrealized Losses			(9)
Fair Value	9,875		12,323
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,334		372
Gross Unrealized Gains	4
Gross Unrealized Losses	(1)		(1)
Fair Value	1,337		371
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	250
Fair Value	250
Variable Rate Demand Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			800
Fair Value			$ 800
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	533
Fair Value	$ 533

Investments - Contractual Matur

Investments - Contractual Maturities of Debt Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Fair Value/Carrying Value	$ 45,116	$ 37,700	$ 37,660
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	1,477
One to two years	2,007
Two to three years	7,013
Three to five years	1,388
Available-for-sale debt securities, Fair Value/Carrying Value	11,885		9,384
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	96
One to two years	1,245
Two to three years	1,246
Three to five years	297
Available-for-sale debt securities, Fair Value/Carrying Value	2,884		930
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	144
One to two years	300
Two to three years	622
Three to five years	3,658
Five to ten years	1,241
More than ten years	743
Available-for-sale debt securities, Fair Value/Carrying Value	6,708		6,890
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	63
One to two years	2,129
Two to three years	2,940
Three to five years	183
Five to ten years	2,095
More than ten years	4,234
Available-for-sale debt securities, Fair Value/Carrying Value	11,644		6,962
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
One to two years	5,122
Two to three years	4,526
Three to five years	227
Available-for-sale debt securities, Fair Value/Carrying Value	9,875		12,323
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	75
One to two years	462
Two to three years	498
Three to five years	302
Available-for-sale debt securities, Fair Value/Carrying Value	1,337		$ 371
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	250
Available-for-sale debt securities, Fair Value/Carrying Value	250
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	533
Available-for-sale debt securities, Fair Value/Carrying Value	$ 533

Investments - Gross Realized Ga

Investments - Gross Realized Gains and Losses on Sale of Debt Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Gross realized gains on debt securities	$ 459	$ 108	$ 57
Gross realized losses on debt securities	(58)	(50)	(592)
Total gain (loss) recognized, net	$ 401	$ 58	$ (535)

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2020
Schedule of Investments [Line Items]
Purchase an available-for-sale debt with credit deterioration		$ 0	$ 0	$ 0
Transfer from investments	$ 3,400,000
Carrying value			3,400,000
Asset impairments		65,000	3,872,000	$ 0
Carrying value of investment		800,000
Note receivable, noncurrent		900,000			$ 900,000
Net Investment Gain (Loss) [Member]
Schedule of Investments [Line Items]
Asset impairments		2,600,000
Other Receivables [Member]
Schedule of Investments [Line Items]
Note receivable, current	$ 4,300,000	4,300,000	4,300,000
Asset impairments		0
Long-term Investments [Member]
Schedule of Investments [Line Items]
Note receivable, noncurrent		$ 900,000	$ 900,000
Investment [Member] | Issuer Concentration [Member] | Market Value of Total Investment Portfolio [Member]
Schedule of Investments [Line Items]
Investment concentration risk percentage		5.00%

Investments - Breakdown of Inve

Investments - Breakdown of Investments with Unrealized Losses (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	$ 3,378	$ 8,965
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(7)	(19)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value		136
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses		(2)
Total Fair Value	3,378	9,101
Total Unrealized Losses	(7)	(21)
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	336	203
Total Fair Value	336	203
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	310	930
Total Fair Value	310	930
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	2	797
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses		(3)
Total Fair Value	2	797
Total Unrealized Losses		(3)
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	2,078	2,594
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(6)	(6)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value		136
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses		(2)
Total Fair Value	2,078	2,730
Total Unrealized Losses	(6)	(8)
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	350	4,070
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses		(9)
Total Fair Value	350	4,070
Total Unrealized Losses		(9)
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value	302	371
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses	(1)	(1)
Total Fair Value	302	371
Total Unrealized Losses	$ (1)	$ (1)

Investments - Realized and Unre

Investments - Realized and Unrealized Gains and Losses for Marketable Equity Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Realized gains (losses) on equity securities sold	$ (2,382)	$ (96)	$ 1,306
Unrealized gains (losses) on equity securities held	6,831	11,472	(4,821)
Total gain (loss) recognized, net	$ 4,449	$ 11,376	$ (3,515)

Investments - Cash Equivalents

Investments - Cash Equivalents and Investments held at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	$ 45,116	$ 37,700	$ 37,660
Marketable equity securities	800
Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Other investments	1,400		2,442
Total	82,217		98,908
Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Other investments	1,400		2,442
Total	46,976		73,571
Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Total	34,708		25,337
Fair Value, Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member]
Schedule of Available-for-sale Securities [Line Items]
Total	533
Money Market Funds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	497		1,309
Money Market Funds [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	497		1,309
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	9,875		12,323
U.S. Government Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	350
Available-for-sale debt securities	9,875		12,323
U.S. Government Bonds [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	350
Available-for-sale debt securities	9,875		12,323
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	11,885		9,384
Corporate Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	11,885		9,384
Corporate Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	11,885		9,384
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	2,884		930
Municipal Fixed-Rate Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	2,884		930
Municipal Fixed-Rate Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	2,884		930
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	6,708		6,890
Asset-Backed Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	6,708		6,890
Asset-Backed Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	6,708		6,890
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	11,644		6,962
Mortgage/Agency-Backed Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	11,644		6,962
Mortgage/Agency-Backed Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	11,644		6,962
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	1,337		371
Foreign Government Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	1,337		371
Foreign Government Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	1,337		371
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	250
Commercial Paper [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	250
Commercial Paper [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	250
Variable Rate Demand Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities			800
Variable Rate Demand Notes [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities			800
Variable Rate Demand Notes [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities			800
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	533
Other Investments [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	533
Other Investments [Member] | Fair Value, Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	533
Marketable Equity Securities - Various Industries [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable equity securities	10,963		35,501
Marketable Equity Securities - Various Industries [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable equity securities	10,963		35,501
Equity in Escrow [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable equity securities			298
Equity in Escrow [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable equity securities			298
Deferred Compensation Plan Assets [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable equity securities	23,891		21,698
Deferred Compensation Plan Assets [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable equity securities	$ 23,891		$ 21,698

Inventory - Components of Inven

Inventory - Components of Inventory, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Raw materials	$ 47,026	$ 36,987
Work in process	776	1,085
Finished goods	77,655	60,233
Total Inventory, net	$ 125,457	$ 98,305

Inventory - Additional Informat

Inventory - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Inventory valuation reserves	$ 39.6	$ 34.1

Property, Plant and Equipment -

Property, Plant and Equipment - Property, Plant and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Land	$ 4,575	$ 4,575
Building and land improvements	35,142	34,797
Building	68,169	68,157
Furniture and fixtures	19,965	19,959
Computer hardware and software	70,942	68,777
Engineering and other equipment	132,920	130,430
Total Property, Plant and Equipment	331,713	326,695
Less: accumulated depreciation	(269,314)	(258,609)
Total Property, Plant and Equipment, net	$ 62,399	$ 68,086

Property, Plant and Equipment_2

Property, Plant and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Asset impairments	$ 65,000	$ 3,872,000	$ 0
Depreciation	$ 12,200,000	$ 12,500,000	$ 12,700,000

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessor and Lessee Lease Description [Line Items]
Operating lease, option to extend, existence	true
Operating lease, option to terminate, existence	true
Short-term lease cost		$ 400,000
Variable lease cost	$ 700,000	900,000
Future operating lease payments	5,554,000		$ 300,000
Allowance for credit losses for our investment in sales type leases	$ 0	$ 0
Minimum [Member]
Lessor and Lessee Lease Description [Line Items]
Operating lease, remaining lease terms	2 months
Operating lease, options to terminate term	3 months
Maximum [Member]
Lessor and Lessee Lease Description [Line Items]
Operating lease, remaining lease terms	55 months
Operating lease, renewal term	2 years
Short-term lease cost	$ 100,000
Lessor sales type lease arrangement terms for network equipments	5 years

Leases - Schedule of Supplement

Leases - Schedule of Supplemental Balance Sheet Information Related to Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
ASSETS
Operating lease assets	$ 5,309	$ 8,452
Operating lease, right-of-use asset, statement of financial position [extensible list]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Liabilities
Current operating lease liability	$ 1,806	$ 2,676
Operating lease, liability, current, statement of financial position [extensible list]	us-gaap:AccruedLiabilitiesAndOtherLiabilities	us-gaap:AccruedLiabilitiesAndOtherLiabilities
Non-current operating lease liability	$ 3,574	$ 5,818
Operating lease, liability, noncurrent, statement of financial position [extensible list]	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Total lease liability	$ 5,380	$ 8,494

Leases - Components of Lease Ex

Leases - Components of Lease Expense included in Consolidated Statement of Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessor Lease Description [Line Items]
Total operating lease expense	$ 2,545	$ 3,881
Cost of Sales [Member]
Lessor Lease Description [Line Items]
Total operating lease expense	113	64
Selling, General and Administrative Expenses [Member]
Lessor Lease Description [Line Items]
Total operating lease expense	1,311	1,400
Research and Development Expenses [Member]
Lessor Lease Description [Line Items]
Total operating lease expense	$ 1,121	$ 2,417

Leases - Schedule of Maturity o

Leases - Schedule of Maturity of Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Lease Liabilities Payments Due [Abstract]
2021	$ 1,895
2022	1,600
2023	1,251
2024	521
2025	287
Total lease payments	5,554		$ 300
Less: Interest	(174)
Present value of lease liabilities	$ 5,380	$ 8,494

Leases - Schedule of Weighted A

Leases - Schedule of Weighted Average Remaining Lease Terms and Weighted Average Discount Rates (Detail)	Dec. 31, 2020	Dec. 31, 2019
USD
Weighted average remaining lease term (years)
Operating leases with functional currency	2 years 4 months 24 days	2 years 7 months 6 days
Weighted average discount rate
Operating leases with functional currency	4.47%	4.02%
Euro
Weighted average remaining lease term (years)
Operating leases with functional currency	3 years 7 months 6 days	4 years 4 months 24 days
Weighted average discount rate
Operating leases with functional currency	1.37%	1.84%

Leases - Schedule of Suppleme_2

Leases - Schedule of Supplemental Cash Flow Information Related to Operating Leases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in the measurement of operating lease assets/liabilities
Cash used in operating activities related to operating leases	$ 2,632	$ 3,439
Right-of-use assets obtained in exchange for operating lease obligations	$ 324	$ 11,615

Leases - Components of Net Inve

Leases - Components of Net Investment in Sales-Type Leases (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Sales Type Leases Net Investment In Leases [Abstract]
Current minimum lease payments receivable	$ 702		$ 1,201
Non-current minimum lease payments receivable	347		889
Total minimum lease payments receivable	1,049		2,090
Less: Current unearned revenue	218		365
Less: Non-current unearned revenue	50		163
Net investment in sales-type leases	$ 781	$ 1,600	$ 1,562

Leases - Schedule of Components

Leases - Schedule of Components of Gross Profit Related to Sales-type Lease and Interest and Dividend Income Included in Consolidated Statements of Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue [Member] | Network Solutions [Member]
Lessor Lease Description [Line Items]
Sales type leases	$ 78	$ 1,723
Cost of Sales [Member] | Network Solutions [Member]
Lessor Lease Description [Line Items]
Sales type leases	32	675
Gross Profit [Member]
Lessor Lease Description [Line Items]
Sales type leases	46	1,048
Interest and Dividend Income [Member]
Lessor Lease Description [Line Items]
Sales type leases	$ 42	$ 357

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Lease Payments to be Received from Sales-Type Leases (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Sales Type And Direct Financing Leases Lease Receivable Fiscal Year Maturity [Abstract]
2021	$ 703
2022	250
2023	88
2024	7
2025	1
Total	$ 1,049

Goodwill - Additional Informati

Goodwill - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill	$ 7,000,000	$ 7,000,000
Impairment charges related to goodwill	0	0	$ 0
Network Solutions [Member]
Goodwill [Line Items]
Goodwill	6,600,000	400,000
Services & Support [Member]
Goodwill [Line Items]
Goodwill	$ 6,600,000	$ 400,000

Intangible Assets - Summary of

Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Finite Lived Intangible Assets [Line Items]
Gross Value	$ 39,293	$ 42,596
Accumulated Amortization	(15,823)	(14,775)
Net Value	23,470	27,821
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Value	21,123	22,356
Accumulated Amortization	(8,055)	(7,233)
Net Value	13,068	15,123
Developed Technology [Member]
Finite Lived Intangible Assets [Line Items]
Gross Value	8,200	10,170
Accumulated Amortization	(2,546)	(3,379)
Net Value	5,654	6,791
Licensed Technology [Member]
Finite Lived Intangible Assets [Line Items]
Gross Value	5,900	5,900
Accumulated Amortization	(1,830)	(1,174)
Net Value	4,070	4,726
Supplier Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Value	2,800	2,800
Accumulated Amortization	(2,800)	(2,508)
Net Value		292
Licensing Agreements [Member]
Finite Lived Intangible Assets [Line Items]
Gross Value	560	560
Accumulated Amortization	(152)	(79)
Net Value	408	481
Patent [Member]
Finite Lived Intangible Assets [Line Items]
Gross Value	500	500
Accumulated Amortization	(294)	(226)
Net Value	206	274
Trade Names [Member]
Finite Lived Intangible Assets [Line Items]
Gross Value	210	310
Accumulated Amortization	(146)	(176)
Net Value	$ 64	$ 134

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Intangible Assets Net Excluding Goodwill [Abstract]
Impairment losses of intangible assets	$ 0	$ 0	$ 0
Amortization expense	$ 4,400,000	$ 5,300,000	$ 2,300,000

Intangible Assets - Estimated F

Intangible Assets - Estimated Future Amortization Expense Related to Intangible Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
2021	$ 4,119
2022	3,494
2023	3,340
2024	3,245
2025	3,031
Thereafter	6,241
Net Value	$ 23,470	$ 27,821

Revolving Credit Agreement - Ad

Revolving Credit Agreement - Additional Information (Detail) - Cadence Bank, N.A [Member] - Secured Revolving Credit Facility [Member] - Revolving Credit and Security Agreement (The “Revolving Credit Agreement”) [Member] - USD ($)	Nov. 04, 2020	Dec. 31, 2020
Line Of Credit Facility [Line Items]
Secured revolving credit facility amount	$ 10,000,000
Credit agreement maturity period	Nov. 4, 2021
Maximum loan to value ratio percentage	75.00%
Maximum interest rate in no event time	1.50%
Borrowings under revolving credit agreement		$ 0
Screen Rate [Member]
Line Of Credit Facility [Line Items]
Debt instrument interest over screen rate	1.50%

Alabama State Industrial Deve_2

Alabama State Industrial Development Authority Financing and Economic Incentives - Additional Information (Detail) - USD ($) $ in Thousands	Jan. 02, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2008	Jan. 13, 1995
Debt Instrument [Line Items]
Proceeds from state industrial development authority issued taxable bonds loaned to ADTRAN			$ 24,600
Repayment of bond		$ 24,600
Payments on long-term debt			1,000	$ 1,100
Total economic incentives realized		$ 0	1,200	$ 1,400
Taxable Revenue Bonds [Member]
Debt Instrument [Line Items]
Proceeds from state industrial development authority issued taxable bonds loaned to ADTRAN			24,600		$ 50,000	$ 20,000
Percentage of interest on bond		2.00%
Maturity date of bond		Jan. 1, 2020
Repayment of bond	$ 24,600
Certificate of deposit			25,600
Payments on long-term debt			$ 1,000

Income Taxes - Summary of Compo

Income Taxes - Summary of Components of Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current
Federal	$ (10,574)	$ (518)	$ (8,001)
State	(329)	(1,065)	(476)
International	3,635	(282)	11,705
Total Current	(7,268)	(1,865)	3,228
Deferred
Federal		24,801	(14,448)
State		5,815	(3,390)
International	(1,356)	(546)	581
Total Deferred	(1,356)	30,070	(17,257)
Total Income Tax Expense (Benefit)	$ (8,624)	$ 28,205	$ (14,029)

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Rate Differs from Federal Statutory Rate (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Tax provision computed at the federal statutory rate	21.00%	21.00%	21.00%
State income tax provision, net of federal benefit	11.10%	6.97%	14.53%
Federal research credits	57.63%	15.53%	14.23%
Foreign taxes	(17.83%)	2.83%	(11.45%)
Tax-exempt income	1.93%	0.49%	0.45%
State tax incentives		3.85%	3.15%
Change in valuation allowance	44.79%	(172.82%)
Foreign tax credits	17.90%	16.69%
Stock-based compensation	(23.36%)	(6.01%)	(2.87%)
Withholding taxes	(20.83%)
Bargain purchase			8.82%
Impact of CARES Act	45.65%
Impact of U.S. tax reform			12.00%
Global intangible low-taxed income ("GILTI")	(0.49%)	(1.87%)	(17.48%)
Other, net	0.56%	(0.49%)	(0.34%)
Effective Tax Rate	138.05%	(113.83%)	42.04%

Income Taxes - Income (Loss) Be

Income Taxes - Income (Loss) Before Expense (Benefit) for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
U.S. entities	$ (12,833)	$ (29,829)	$ (74,131)
International entities	6,587	5,052	40,760
Loss Before Income Taxes	$ (6,246)	$ (24,777)	$ (33,371)

Income Taxes - Significant Comp

Income Taxes - Significant Components of Current and Non-current Deferred Taxes (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Inventory	$ 8,882	$ 7,144
Accrued expenses	2,331	2,330
Deferred compensation	6,714	5,660
Stock-based compensation	1,971	2,451
Uncertain tax positions related to state taxes and related interest	149	241
Pensions	8,554	7,074
Foreign losses	2,590	2,925
State losses and credit carry-forwards	5,509	3,995
Federal loss and research carry-forwards	17,323	12,171
Lease liabilities	1,588	2,496
Capitalized research and development expenditures	11,832	22,230
Valuation allowance	(45,818)	(48,616)
Total Deferred Tax Assets	21,625	20,101
Property, plant and equipment	(4,546)	(2,815)
Intellectual property	(4,375)	(5,337)
Right of use lease assets	(1,585)	(2,496)
Investments	(1,250)	(1,892)
Total Deferred Tax Liabilities	(11,756)	(12,540)
Net Deferred Tax Assets	$ 9,869	$ 7,561

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Income tax benefit, result of CARES act of 2020	$ 10,800,000
Valuation allowance established against deferred tax assets	7,900,000
Tax rate differential on carrying back losses amount	$ 2,900,000
US corporate tax rate	35.00%
Federal tax rate	21.00%	21.00%	21.00%
Deferred tax benefit recorded as an adjustment to other comprehensive income	$ 100,000	$ 400,000
Deferred tax assets, gross	55,687,000	56,177,000
Valuation allowance established against deferred tax assets	45,818,000	48,616,000
Deferred tax assets tax credit carryforward net operating loss and research and development	2,000,000
Decrease in valuation allowance	2,800,000
Deferred tax assets tax credit carryforward claims related to CARES Act	7,900,000
Net of deferred tax liabilities	9,869,000	7,561,000
Foreign and domestic loss carry-forwards, research and development tax credits, unamortized research and development cost and state credit carry-forwards	$ 37,300,000	41,300,000
Operating loss carry forwards expiration year	2029
Deferred tax assets	$ 21,625,000	20,101,000
Cash and cash equivalents	60,161,000	73,773,000
Short-term investments (includes $1,731 and $5,201 of available-for-sale securities as of December 31, 2020 and 2019, respectively, reported at fair value)	3,131,000	33,243,000
Short-term liquidity amount	63,300,000	107,000,000
Withholding tax liabilities in jurisdiction	700,000
Income tax benefit (expense) from stock options exercised adjustment to equity	0	0	$ 0
Unrecognized tax benefits	1,078,000	1,487,000	1,868,000	$ 2,366,000
Unrecognized tax benefits, effective tax rate	1,000,000	1,400,000	1,700,000
Accrued interest and penalties	300,000	500,000	$ 700,000
Foreign Subsidiaries [Member]
Income Tax Disclosure [Line Items]
Short-term liquidity amount	$ 49,700,000	$ 52,300,000
Short-term liquidity, in percentage	78.50%	48.90%
Operating Losses Expiration Between 2020 and 2039 [Member]
Income Tax Disclosure [Line Items]
Deferred tax assets	$ 25,100,000
Minimum [Member]
Income Tax Disclosure [Line Items]
Operating loss carry forwards expiration year	2021
Maximum [Member]
Income Tax Disclosure [Line Items]
Operating loss carry forwards expiration year	2040
Domestic [Member]
Income Tax Disclosure [Line Items]
Deferred tax assets, gross	$ 43,791,000	$ 46,266,000
Valuation allowance established against deferred tax assets	43,791,000	$ 46,266,000
Current valuation allowance established against deferred tax assets	$ 43,800,000

Income Taxes - Summary of Suppl

Income Taxes - Summary of Supplemental Balance Sheet Information Related to Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets	$ 55,687	$ 56,177
Valuation allowance	(45,818)	(48,616)
Net Deferred Tax Assets	9,869	7,561
Domestic [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets	43,791	46,266
Valuation allowance	(43,791)	(46,266)
International [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets	11,896	9,911
Valuation allowance	(2,027)	(2,350)
Net Deferred Tax Assets	$ 9,869	$ 7,561

Income Taxes - Change in Unreco

Income Taxes - Change in Unrecognized Income Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Balance at beginning of period	$ 1,487	$ 1,868	$ 2,366
Increases for tax position related to, Prior years	4		3
Increases for tax position related to, Current year	165	161	254
Decreases for tax positions related to, Prior years		(71)
Expiration of applicable statute of limitations	(578)	(471)	(755)
Balance at end of period	$ 1,078	$ 1,487	$ 1,868

Employee Benefit Plans (Pension

Employee Benefit Plans (Pension Benefit Plan) - Schedule of Pension Benefit Plan Obligations and Funded Status (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in projected benefit obligation:
Projected benefit obligation at beginning of period	$ 43,902	$ 37,245
Service cost	1,270	1,471	$ 1,193
Interest cost	444	634	727
Actuarial (gain) loss - experience	(744)	453
Actuarial loss - assumptions	2,458	5,091
Benefit payments	(509)	(166)
Effects of foreign currency exchange rate changes	4,106	(826)
Projected benefit obligation at end of period	50,927	43,902	37,245
Change in plan assets:
Fair value of plan assets at beginning of period	28,016	24,159
Actual gain on plan assets	1,744	4,392
Contributions	24
Effects of foreign currency exchange rate changes	2,479	(535)
Fair value of plan assets at end of period	32,263	28,016	$ 24,159
Unfunded status at end of period	$ (18,664)	$ (15,886)

Employee Benefit Plans (Pensi_2

Employee Benefit Plans (Pension Benefit Plan) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 50.9	$ 43.9
Bond Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of target allocation ranges by asset class	50.00%
Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of target allocation ranges by asset class	40.00%
Cash, Real Estate, and Managed Futures [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of target allocation ranges by asset class	10.00%
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Threshold for unamortized gain losses	10.00%

Employee Benefit Plans (Pensi_3

Employee Benefit Plans (Pension Benefit Plan) - Summary of Net Amounts Recognized in Consolidated Balance Sheets for the Unfunded Pension Liability (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Current liability	$ 0	$ 0
Pension liability	18,664	15,886
Total	$ 18,664	$ 15,886

Employee Benefit Plans (Pensi_4

Employee Benefit Plans (Pension Benefit Plan) - Components of Net Periodic Pension Cost and Amounts Recognized Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net periodic benefit cost:
Service cost	$ 1,270	$ 1,471	$ 1,193
Interest cost	444	634	727
Expected return on plan assets	(1,679)	(1,392)	(1,548)
Amortization of actuarial losses	970	795	247
Net periodic benefit cost	1,005	1,508	619
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Net actuarial (gain) loss	1,784	2,488	5,638
Amortization of actuarial losses	(1,212)	(771)	(196)
Amount recognized in other comprehensive income (loss)	572	1,717	5,442
Total recognized in net periodic benefit cost and other comprehensive income (loss)	$ 1,577	$ 3,225	$ 6,061

Employee Benefit Plans (Pensi_5

Employee Benefit Plans (Pension Benefit Plan) - Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Net actuarial loss	$ (13,545)	$ (12,973)

Employee Benefit Plans (Pensi_6

Employee Benefit Plans (Pension Benefit Plan) - Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Discount rate	1.00%	1.75%	2.13%
Rate of compensation increase	2.00%	2.00%	2.00%
Expected long-term rates of return	5.90%	5.90%	5.90%

Employee Benefit Plans (Pensi_7

Employee Benefit Plans (Pension Benefit Plan) - Weighted-Average Assumptions Used to Determine Benefit Obligation (Detail)	Dec. 31, 2020	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Discount rate	0.69%	1.00%
Rate of compensation increase	2.00%	2.00%

Employee Benefit Plans (Pensi_8

Employee Benefit Plans (Pension Benefit Plan) - Schedule of Pension Benefit Payments Expected Future Service (Detail) $ in Thousands	Dec. 31, 2020USD ($)
Compensation And Retirement Disclosure [Abstract]
2021	$ 714
2022	1,048
2023	1,348
2024	1,657
2025	1,621
2026 - 2030	7,615
Total	$ 14,003

Employee Benefit Plans (Pensi_9

Employee Benefit Plans (Pension Benefit Plan) - Schedule of Cash Equivalents and Investments Held at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 32,263	$ 28,016	$ 24,159
Pension Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32,263	28,016
Pension Benefit Plan [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,935	691
Pension Benefit Plan [Member] | Available-For-Sale Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30,328	27,325
Pension Benefit Plan [Member] | Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,971	6,645
Pension Benefit Plan [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,746	5,514
Pension Benefit Plan [Member] | Emerging Markets Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	307	531
Pension Benefit Plan [Member] | Global Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11,638	11,071
Pension Benefit Plan [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,848	956
Pension Benefit Plan [Member] | Balanced Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,515	863
Pension Benefit Plan [Member] | Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	198	312
Pension Benefit Plan [Member] | Global Real Estate Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	799	902
Pension Benefit Plan [Member] | Managed Futures Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	306	531
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	32,263	28,016
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,935	691
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Available-For-Sale Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30,328	27,325
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,971	6,645
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,746	5,514
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Emerging Markets Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	307	531
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Global Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11,638	11,071
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,848	956
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Balanced Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,515	863
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Large Cap Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	198	312
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Global Real Estate Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	799	902
Pension Benefit Plan [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Managed Futures Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 306	$ 531

Employee Benefit Plans (401(k)

Employee Benefit Plans (401(k) Savings Plan) - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Criteria of employer to contribute in employee saving plan	100% of an employee’s first 3% of contributions and 50% of their next 2% of contributions
Percentage of employer match to employee's contribution	100.00%
Percentage of employer match to employee's contribution	50.00%
Upper limit of employer match	4.00%
Percentage of employee first contribution	3.00%
Percentage of employee second contribution	2.00%
Maximum statutory compensation under code	$ 285,000
Contribution expense and plan administration costs for savings plan	$ 4,000,000	$ 4,400,000	$ 4,400,000

Employee Benefit Plans (Deferre

Employee Benefit Plans (Deferred Compensation Plans) - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)Compensation_Program	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Deferred Compensation Arrangement With Individual Postretirement Benefits [Line Items]
Number of deferred compensation programs | Compensation_Program	4
Maximum percentage of cash compensation allowed to be deferred under the deferred compensation plan	25.00%
Criteria for benefit distribution	six months after termination of employment in a single lump sum payment or annual installments paid over a three or ten-year term based on the participant’s election
Benefit distribution, scheduled to be distributed term	6 months
Deferred compensation income (expense) adjustments due to fair value of the trust assets	$ 4.3	$ 3.6	$ (2.1)
Treasury Stock [Member]
Deferred Compensation Arrangement With Individual Postretirement Benefits [Line Items]
Common stock, value of shares held by trust	$ 2.8
Minimum [Member]
Deferred Compensation Arrangement With Individual Postretirement Benefits [Line Items]
Benefit distribution, paid over annual instalment term	3 years
Maximum [Member]
Deferred Compensation Arrangement With Individual Postretirement Benefits [Line Items]
Benefit distribution, paid over annual instalment term	10 years

Employee Benefit Plans (Defer_2

Employee Benefit Plans (Deferred Compensation Plans) - Fair Value of Assets Held by Trust and Amounts Payable to Plan Participants (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Long-term Investments	$ 23,891	$ 21,698
Amounts Payable to Plan Participants Deferred Compensation Liability	25,866	21,698
Deferred Compensation Plan Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Long-term investments	23,891	21,698
Deferred Compensation Liability [Member]
Defined Benefit Plan Disclosure [Line Items]
Amounts Payable to Plan Participants Deferred Compensation Liability	$ 25,866	$ 21,698

Employee Benefit Plans (Retiree

Employee Benefit Plans (Retiree Medical Coverage) - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Maximum number of years medical, dental and prescription drug coverage to spouses of retired former officers	30 years
Total liability recorded to provide medical, dental and prescription drug coverage	$ 0.2	$ 0.1

Segment Information and Major_3

Segment Information and Major Customers - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)CustomerCategorySegment	Dec. 31, 2019USD ($)Customer	Dec. 31, 2018Customer
Segment Reporting Information [Line Items]
Number of reportable segments | Segment	2
Number of categories | Category	3
Number of single customer comprising more than 10% of sales | Customer	3	3	2
Long-lived assets	$ 62.4	$ 68.1
U.S. [Member]
Segment Reporting Information [Line Items]
Long-lived assets	58.4	64.2
Outside U.S. [Member]
Segment Reporting Information [Line Items]
Long-lived assets	$ 4	$ 3.9
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Customer 1 [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	15.00%	19.00%	27.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Customer 2 [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	12.00%	17.00%	17.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Customer 3 [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	10.00%	13.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | The Five Largest Customers Other Than Those With More Than 10% Of Revenues and Excluding Distributors [Member]
Segment Reporting Information [Line Items]
Concentration risk, percentage	19.00%	15.00%	18.00%

Segment Information and Major_4

Segment Information and Major Customers - Sales and Gross Profit of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenue	$ 130,129	$ 133,143	$ 128,715	$ 114,523	$ 115,787	$ 114,092	$ 156,391	$ 143,791	$ 506,510	$ 530,061	$ 529,277
Gross Profit	$ 53,517	$ 58,962	$ 53,472	$ 51,600	$ 47,209	$ 46,331	$ 65,015	$ 60,612	217,551	219,167	203,565
Network Solutions [Member]
Segment Reporting Information [Line Items]
Revenue									438,015	455,226	458,232
Gross Profit									193,789	191,549	179,303
Services & Support [Member]
Segment Reporting Information [Line Items]
Revenue									68,495	74,835	71,045
Gross Profit									$ 23,762	$ 27,618	$ 24,262

Segment Information and Major_5

Segment Information and Major Customers - Disaggregation of Sales by Category (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Revenue	$ 130,129	$ 133,143	$ 128,715	$ 114,523	$ 115,787	$ 114,092	$ 156,391	$ 143,791	$ 506,510	$ 530,061	$ 529,277
Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue									438,015	455,226	458,232
Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue									68,495	74,835	71,045
Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue									313,138	348,874	358,870
Access & Aggregation [Member] | Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue									262,578	289,980	301,801
Access & Aggregation [Member] | Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue									50,560	58,894	57,069
Subscriber Solutions & Experience [Member]
Disaggregation Of Revenue [Line Items]
Revenue									171,087	152,920	134,460
Subscriber Solutions & Experience [Member] | Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue									161,824	144,651	129,067
Subscriber Solutions & Experience [Member] | Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue									9,263	8,269	5,393
Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue									22,285	28,267	35,947
Traditional & Other Products [Member] | Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue									13,613	20,595	27,364
Traditional & Other Products [Member] | Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue									$ 8,672	$ 7,672	$ 8,583

Segment Information and Major_6

Segment Information and Major Customers - Sales Information by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from External Customer [Line Items]
Revenue	$ 130,129	$ 133,143	$ 128,715	$ 114,523	$ 115,787	$ 114,092	$ 156,391	$ 143,791	$ 506,510	$ 530,061	$ 529,277
United States [Member]
Revenue from External Customer [Line Items]
Revenue									352,079	300,853	288,843
Germany [Member]
Revenue from External Customer [Line Items]
Revenue									74,882	78,062	167,251
Mexico [Member]
Revenue from External Customer [Line Items]
Revenue									4,087	90,795	12,186
Other International [Member]
Revenue from External Customer [Line Items]
Revenue									$ 75,462	$ 60,351	$ 60,997

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Mar. 31, 2020Officer	Oct. 17, 2019Officer	Dec. 31, 2020USD ($)	Mar. 31, 2021USD ($)	Dec. 31, 2019USD ($)
Contingencies And Commitments [Line Items]
Commitments related to performance bonds			$ 15,200,000		$ 9,300,000
Commitments related to performance bonds expiration month and year			2024-08
Letter of credit secured by pledge of a portion of fixed income securities			$ 11,200,000
Commitments towards private equity funds			4,900,000
Investment Commitments [Member]
Contingencies And Commitments [Line Items]
Aggregate investment committed in private equity funds			5,000,000
Long-term Investments [Member]
Contingencies And Commitments [Line Items]
Letter of credit secured by pledge of a portion of fixed income securities			11,200,000
Minimum [Member]
Contingencies And Commitments [Line Items]
Collateral value required to be maintained			9,000,000
Maximum [Member] | Scenario Forecast [Member]
Contingencies And Commitments [Line Items]
Collateral value required to be maintained				$ 15,000,000
Maximum [Member] | Restricted Cash [Member]
Contingencies And Commitments [Line Items]
Letter of credit secured by pledge of a portion of fixed income securities			$ 100,000
Current Executive Officers [Member]
Contingencies And Commitments [Line Items]
Number of officers | Officer	2	2
Former Executive Officers [Member]
Contingencies And Commitments [Line Items]
Number of officers | Officer	1	1

Current Expected Credit Losse_2

Current Expected Credit Losses - Additional Information (Detail)	Jan. 01, 2020USD ($)	Dec. 31, 2020USD ($)Position	Dec. 31, 2019USD ($)
Financing Receivable Allowance For Credit Losses [Line Items]
Accounts receivable	$ 90,500,000	$ 98,827,000	$ 90,531,000
Allowance for credit loss, accounts receivable	0	0
Allowance for credit losses, accounts receivable		38,000	38,000
Outstanding contract asset	2,800,000	63,000	2,812,000
Allowance for credit losses related to contract assets	0	0
Outstanding net investment in sales-type leases	1,600,000	781,000	1,562,000
Net investment in sales-type leases, allowance for credit loss	0	0
Secured loan receivable	900,000	900,000
Accrued interest receivable	100,000	100,000
Secured loan receivable, allowance for credit loss	0	0
Available-for-sale debt securities	37,700,000	$ 45,116,000	37,660,000
Number of positions in available-for-sale debt securities, unrealized loss position | Position		42
Available-for-sale, debt securities, allowance for credit loss	0	$ 0
Secured Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loss related to secured loan receivable		0
Maximum [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses, accounts receivable		100,000	$ 100,000
Maximum [Member] | Secured Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Accrued interest receivable	$ 100,000	$ 100,000

Current Expected Credit Losse_3

Current Expected Credit Losses - Amortized Cost Basis in Sales-Type Leases based on Payment Activity (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Sales Type Lease Net Investment In Lease Credit Quality Indicator [Line Items]
2020	$ 55
2019	192
2018	354
2017	128
2016	52
Net investment in sales-type leases	781	$ 1,600	$ 1,562
Payment Performance Performing [Member]
Sales Type Lease Net Investment In Lease Credit Quality Indicator [Line Items]
2020	55
2019	192
2018	354
2017	128
2016	52
Net investment in sales-type leases	$ 781

Earnings (Loss) Per Share - Sum

Earnings (Loss) Per Share - Summary of Calculations of Basic and Diluted Earnings (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator
Net Income (Loss)	$ 6,114	$ 5,481	$ 752	$ (9,969)	$ (11,624)	$ (46,123)	$ 3,995	$ 770	$ 2,378	$ (52,982)	$ (19,342)
Denominator
Weighted average number of shares – basic									47,996	47,836	47,880
Effect of dilutive securities:
PSUs, RSUs and restricted stock									292
Weighted average number of shares – diluted									48,288	47,836	47,880
Earnings (loss) per share – basic	$ 0.13	$ 0.11	$ 0.02	$ (0.21)	$ (0.25)	$ (0.96)	$ 0.08	$ 0.02	$ 0.05	$ (1.11)	$ (0.40)
Earnings (loss) per share – diluted	$ 0.13	$ 0.11	$ 0.02	$ (0.21)	$ (0.25)	$ (0.96)	$ 0.08	$ 0.02	$ 0.05	$ (1.11)	$ (0.40)

Earnings (Loss) Per Share - Add

Earnings (Loss) Per Share - Additional Information (Detail) - shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive effect excluded calculation of diluted earnings (loss) per share	3.6	5.2
Unvested Stock Options, PSUs, RSUs and Restricted Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive effect excluded calculation of diluted earnings (loss) per share	0.1	0.5

Restructuring - Additional Info

Restructuring - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2018
Restructuring And Related Activities [Abstract]
Cumulative amount of restructuring expenses incurred for restructuring plan	$ 12.2	$ 7.3

Restructuring - Schedule of Rec

Restructuring - Schedule of Reconciliation of Restructuring Liability (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring And Related Activities [Abstract]
Balance at beginning of period	$ 1,568	$ 185
Plus: Amounts charged to cost and expense	6,229	6,014	$ 7,261
Less: Amounts paid	(3,611)	(4,631)
Balance at end of period	$ 4,186	$ 1,568	$ 185

Restructuring - Schedule of Com

Restructuring - Schedule of Components of Restructuring Expense Included in Consolidated Statements of Income (Loss) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	$ 6,229	$ 6,014	$ 7,261
Selling, General and Administrative Expenses [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	1,832	2,360	2,655
Research and Development Expenses [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	3,942	2,869	1,831
Cost of Sales [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	$ 455	$ 785	$ 2,775

Restructuring - Schedule of C_2

Restructuring - Schedule of Components of Restructuring Expense by Geographic Area (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	$ 6,229	$ 6,014	$ 7,261
United States [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	2,234	3,336	7,120
International [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	$ 3,995	$ 2,678	$ 141

Summarized Quarterly Financia_3

Summarized Quarterly Financial Data (Unaudited) - Quarterly Operating Results (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total Sales	$ 130,129	$ 133,143	$ 128,715	$ 114,523	$ 115,787	$ 114,092	$ 156,391	$ 143,791	$ 506,510	$ 530,061	$ 529,277
Gross Profit	53,517	58,962	53,472	51,600	47,209	46,331	65,015	60,612	217,551	219,167	203,565
Operating Income (Loss)	(3,324)	4,534	(6,039)	(4,944)	(14,070)	(20,288)	562	(6,167)	(9,773)	(39,963)	(45,422)
Net Income (Loss)	$ 6,114	$ 5,481	$ 752	$ (9,969)	$ (11,624)	$ (46,123)	$ 3,995	$ 770	$ 2,378	$ (52,982)	$ (19,342)
Earnings (loss) per common share - basic	$ 0.13	$ 0.11	$ 0.02	$ (0.21)	$ (0.25)	$ (0.96)	$ 0.08	$ 0.02	$ 0.05	$ (1.11)	$ (0.40)
Earnings (loss) per common share - diluted	$ 0.13	$ 0.11	$ 0.02	$ (0.21)	$ (0.25)	$ (0.96)	$ 0.08	$ 0.02	$ 0.05	$ (1.11)	$ (0.40)

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($)	Feb. 03, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 04, 2021
Subsequent Event [Line Items]
Common stock dividends per share declared		$ 0.09	$ 0.09	$ 0.09
Minimum [Member]
Subsequent Event [Line Items]
Collateral value required to be maintained		$ 9,000,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declaration date	Feb. 3, 2021
Common stock dividends per share declared	$ 0.09
Dividend record date	Feb. 18, 2021
Dividend payment date	Mar. 4, 2021
Quarterly dividend payable, aggregate amount					$ 4,400,000
Subsequent Event [Member] | Maximum [Member]
Subsequent Event [Line Items]
Collateral value required to be maintained	$ 15,000,000

Schedule II - Valuation and Q_2

Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 38	$ 128
Charged to costs & expenses		38	$ 128
Deductions		128
Balance at end of period	38	38	128
Inventory Reserve [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	34,162	30,009	23,355
Charged to costs & expenses	11,404	5,893	7,006
Deductions	6,005	1,740	352
Balance at end of period	39,561	34,162	30,009
Warranty Liability [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	8,394	8,623	9,724
Charged to costs & expenses	1,538	4,569	7,392
Deductions	2,786	4,798	8,493
Balance at end of period	7,146	8,394	8,623
Deferred Tax Asset Valuation Allowance [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	48,616	5,816	6,006
Charged to costs & expenses	5,120	43,560
Deductions	7,918	760	190
Balance at end of period	$ 45,818	$ 48,616	$ 5,816