ADTRAN (ADTN) 10-Q 6 Aug 21 2021 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Aug. 04, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Entity Registrant Name	ADTRAN, Inc.
Trading Symbol	ADTN
Entity Central Index Key	0000926282
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		48,561,812
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
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 Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, Par Value $0.01 per share
Security Exchange Name	NASDAQ

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current Assets
Cash and cash equivalents	$ 69,927	$ 60,161
Restricted cash	54	18
Short-term investments (includes $1,418 and $1,731 of available-for-sale securities as of June 30, 2021 and December 31, 2020, respectively, reported at fair value)	2,818	3,131
Accounts receivable, less allowance for expected credit losses of $0 as of June 30, 2021 and $38 as of December 31, 2020	122,669	98,827
Other receivables	20,187	21,531
Inventory, net	119,012	125,457
Prepaid expenses and other current assets	9,830	8,293
Total Current Assets	344,497	317,418
Property, plant and equipment, net	58,270	62,399
Deferred tax assets, net	9,165	9,869
Goodwill	6,968	6,968
Intangibles, net	21,354	23,470
Other assets	28,394	25,425
Long-term investments (includes $43,062 and $43,385 of available-for-sale securities as of June 30, 2021 and December 31, 2020, respectively, reported at fair value)	82,778	80,130
Total Assets	551,426	525,679
Current Liabilities
Accounts payable	66,499	49,929
Unearned revenue	15,889	14,092
Accrued expenses and other liabilities	15,655	13,609
Accrued wages and benefits	15,681	15,262
Income tax payable, net	2,345	1,301
Total Current Liabilities	116,069	94,193
Non-current unearned revenue	7,030	6,888
Pension liability	17,566	18,664
Deferred compensation liability	28,769	25,866
Other non-current liabilities	6,477	7,124
Total Liabilities	175,911	152,735
Commitments and contingencies (see Note 18)
Stockholders’ Equity
Common stock, par value $0.01 per share; 200,000 shares authorized; 79,652 shares issued and 48,524 shares outstanding as of June 30, 2021 and 79,652 shares issued and 48,241 shares outstanding as of December 31, 2020	797	797
Additional paid-in capital	285,081	281,466
Accumulated other comprehensive loss	(13,140)	(11,639)
Retained earnings	776,054	781,813
Treasury stock at cost: 31,128 and 31,280 shares at June 30, 2021 and December 31, 2020, respectively	(673,277)	(679,493)
Total Stockholders’ Equity	375,515	372,944
Total Liabilities and Stockholders’ Equity	$ 551,426	$ 525,679

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Short term investments, available-for-sale securities at fair value	$ 1,418	$ 1,731
Accounts receivable, allowance for expected credit losses	0	38
Long Term Investments, available-for-sale securities Fair Value	$ 43,062	$ 43,385
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	48,524,000	48,241,000
Treasury stock, shares	31,128,000	31,280,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue
Total Revenue	$ 143,232	$ 128,715	$ 270,765	$ 243,238
Cost of Revenue
Total Cost of Revenue	80,564	75,243	154,496	138,166
Gross Profit	62,668	53,472	116,269	105,072
Selling, general and administrative expenses	30,866	30,799	58,301	57,419
Research and development expenses	27,871	28,712	55,372	58,571
Asset impairments				65
Operating Income (Loss)	3,931	(6,039)	2,596	(10,983)
Interest and dividend income	253	331	543	687
Interest expense	(6)		(12)	(1)
Net investment gain (loss)	2,009	9,852	3,005	(1,025)
Other income (expense), net	26	(1,757)	2,025	(628)
Income (Loss) Before Income Taxes	6,213	2,387	8,157	(11,950)
Income tax (expense) benefit	(1,127)	(1,635)	(2,175)	2,733
Net Income (Loss)	$ 5,086	$ 752	$ 5,982	$ (9,217)
Weighted average shares outstanding – basic	48,449	47,958	48,393	47,957
Weighted average shares outstanding – diluted	49,426	48,254	49,225	47,957
Earnings (loss) per common share – basic	$ 0.10	$ 0.02	$ 0.12	$ (0.19)
Earnings (loss) per common share – diluted	$ 0.10	$ 0.02	$ 0.12	$ (0.19)
Network Solutions [Member]
Revenue
Total Revenue	$ 125,449	$ 111,323	$ 239,258	$ 208,695
Cost of Revenue
Total Cost of Revenue	70,014	64,071	135,015	115,697
Gross Profit	55,435	47,252	104,243	92,998
Services & Support [Member]
Revenue
Total Revenue	17,783	17,392	31,507	34,543
Cost of Revenue
Total Cost of Revenue	10,550	11,172	19,481	22,469
Gross Profit	$ 7,233	$ 6,220	$ 12,026	$ 12,074

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net Income (Loss)	$ 5,086	$ 752	$ 5,982	$ (9,217)
Other Comprehensive Income (Loss), net of tax
Net unrealized gain (loss) on available-for-sale securities	(95)	373	(287)	490
Defined benefit plan adjustments	212	191	311	332
Foreign currency translation	338	1,899	(1,525)	249
Other Comprehensive Income (Loss), net of tax	455	2,463	(1,501)	1,071
Comprehensive Income (Loss), net of tax	$ 5,541	$ 3,215	$ 4,481	$ (8,146)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Dec. 31, 2019	$ 380,426	$ 797	$ 274,632	$ 806,702	$ (685,288)	$ (16,417)
Beginning Balance, Shares at Dec. 31, 2019		79,652
Net Income (Loss)	(9,969)			(9,969)
Other comprehensive income (loss), net of tax	(1,392)					(1,392)
Dividend payments ($0.09 per share)	(4,328)			(4,328)
Dividends accrued on unvested RSUs	(32)			(32)
Deferred compensation adjustments, net of tax	(2,758)				(2,758)
PSUs, RSUs and restricted stock vested	(23)			(1,524)	1,501
Stock-based compensation expense	1,791		1,791
Ending Balance at Mar. 31, 2020	363,715	$ 797	276,423	790,849	(686,545)	(17,809)
Ending Balance, Shares at Mar. 31, 2020		79,652
Beginning Balance at Dec. 31, 2019	380,426	$ 797	274,632	806,702	(685,288)	(16,417)
Beginning Balance, Shares at Dec. 31, 2019		79,652
Net Income (Loss)	(9,217)
Other comprehensive income (loss), net of tax	1,071
Ending Balance at Jun. 30, 2020	364,194	$ 797	278,078	787,220	(686,555)	(15,346)
Ending Balance, Shares at Jun. 30, 2020		79,652
Beginning Balance at Mar. 31, 2020	363,715	$ 797	276,423	790,849	(686,545)	(17,809)
Beginning Balance, Shares at Mar. 31, 2020		79,652
Net Income (Loss)	752			752
Other comprehensive income (loss), net of tax	2,463					2,463
Dividend payments ($0.09 per share)	(4,337)			(4,337)
Dividends accrued on unvested RSUs	(28)			(28)
Deferred compensation adjustments, net of tax	(24)				(24)
PSUs, RSUs and restricted stock vested	(2)			(16)	14
Stock-based compensation expense	1,655		1,655
Ending Balance at Jun. 30, 2020	364,194	$ 797	278,078	787,220	(686,555)	(15,346)
Ending Balance, Shares at Jun. 30, 2020		79,652
Beginning Balance at Dec. 31, 2020	$ 372,944	$ 797	281,466	781,813	(679,493)	(11,639)
Beginning Balance, Shares at Dec. 31, 2020	79,652	79,652
Net Income (Loss)	$ 896			896
Other comprehensive income (loss), net of tax	(1,956)					(1,956)
Dividend payments ($0.09 per share)	(4,361)			(4,361)
Dividends accrued on unvested RSUs	(68)			(68)
Deferred compensation adjustments, net of tax	(50)				(50)
PSUs, RSUs and restricted stock vested	(81)			(1,683)	1,602
Stock options exercised	1,244			(476)	1,720
Stock-based compensation expense	1,807		1,807
Ending Balance at Mar. 31, 2021	370,375	$ 797	283,273	776,121	(676,221)	(13,595)
Ending Balance, Shares at Mar. 31, 2021		79,652
Beginning Balance at Dec. 31, 2020	$ 372,944	$ 797	281,466	781,813	(679,493)	(11,639)
Beginning Balance, Shares at Dec. 31, 2020	79,652	79,652
Net Income (Loss)	$ 5,982
Other comprehensive income (loss), net of tax	(1,501)
Ending Balance at Jun. 30, 2021	$ 375,515	$ 797	285,081	776,054	(673,277)	(13,140)
Ending Balance, Shares at Jun. 30, 2021	79,652	79,652
Beginning Balance at Mar. 31, 2021	$ 370,375	$ 797	283,273	776,121	(676,221)	(13,595)
Beginning Balance, Shares at Mar. 31, 2021		79,652
Net Income (Loss)	5,086			5,086
Other comprehensive income (loss), net of tax	455					455
Dividend payments ($0.09 per share)	(4,374)			(4,374)
Dividends accrued on unvested RSUs	(128)			(128)
Deferred compensation adjustments, net of tax	(12)				(12)
PSUs, RSUs and restricted stock vested	(3)			(32)	29
Stock options exercised	2,308			(619)	2,927
Stock-based compensation expense	1,808		1,808
Ending Balance at Jun. 30, 2021	$ 375,515	$ 797	$ 285,081	$ 776,054	$ (673,277)	$ (13,140)
Ending Balance, Shares at Jun. 30, 2021	79,652	79,652

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020
Statement Of Stockholders Equity [Abstract]
Dividend payments	$ 0.09	$ 0.09	$ 0.09	$ 0.09

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Cash flows from operating activities:
Net income (loss)	$ 5,982	$ (9,217)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	8,232	8,404
(Gain) loss on investments	(3,255)	1,025
Stock-based compensation expense	3,615	3,446
Deferred income taxes	441	(5)
Other	53	138
Asset impairments		65
Changes in operating assets and liabilities:
Accounts receivable, net	(24,322)	(4,727)
Other receivables	1,412	(9,468)
Inventory, net	5,940	(7,878)
Prepaid expenses, other current assets and other assets	(4,767)	1,444
Accounts payable	16,814	17,389
Accrued expenses and other liabilities	6,999	2,097
Income taxes payable, net	1,069	(1,032)
Net cash provided by operating activities	18,213	1,681
Cash flows from investing activities:
Purchases of property, plant and equipment	(2,210)	(3,148)
Proceeds from sales and maturities of available-for-sale investments	20,597	63,318
Purchases of available-for-sale investments	(20,121)	(31,897)
Acquisition of note receivable		(523)
Net cash provided by (used in) investing activities	(1,734)	27,750
Cash flows from financing activities:
Proceeds from stock option exercises	3,552
Tax withholdings related to stock-based compensation settlements	(113)
Dividend payments	(8,735)	(8,665)
Repayment of bonds payable		(24,600)
Net cash used in financing activities	(5,296)	(33,265)
Net increase (decrease) in cash, cash equivalents and restricted cash	11,183	(3,834)
Effect of exchange rate changes	(1,381)	306
Cash, cash equivalents and restricted cash, beginning of period	60,179	73,773	$ 73,773
Cash, cash equivalents and restricted cash, end of period	69,981	70,245	$ 60,179
Supplemental disclosure of non-cash investing activities:
Right-of-use assets obtained in exchange for lease obligations	275	93
Purchases of property, plant and equipment included in accounts payable	$ 144	$ 198

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying unaudited condensed consolidated financial statements of ADTRAN ® In the opinion of management, all adjustments necessary to fairly state these interim statements have been recorded and are of a normal and recurring nature. The results of operations for an interim period are not necessarily indicative of the results for the full year. The interim financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in ADTRAN’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on February 26, 2021. 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 expense during the reporting period. The more significant estimates include excess and obsolete inventory reserves, warranty reserves, customer rebates, determination and accrual of deferred revenue components of multi-element sales agreements, estimated costs to complete obligations associated with deferred and accrued 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 and fair value of investments. 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 SARS-CoV-2 coronavirus/COVID-19 global pandemic (or variants of the SARS-CoV-2 coronavirus, including the Delta variant) as of June 30, 2021 and through the date of this report. The accounting matters assessed included, but were not limited to, the allowance for expected credit losses, stock-based compensation, 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 six months ended June 30, 2021 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 an Immaterial Misstatement During the three months ended March 31, 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 l ong-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 by remeasuring the investment assets to their historical cost basis through the recording of a n et investment gain of $ 1.5 million in the unaudited Condensed Consolidated Statement of Income (Loss) and then correcting the classification by decreasing the l ong-term investment balance at its remeasured cost basis of $ 2.8 million to Treasury stock in the unaudited Condensed Consolidated Balance Sheet as of March 31, 2020. Management has determined that this misstatement was not material to any of its previously issued financial statements and that the correction of the misstatement was not material to the Company’s 2020 annual financial results on either a quantitative or qualitative basis. Recently Adopted Accounting Pronouncements We recently adopted the following accounting standards, which had the following impacts on our condensed consolidated financial statements: 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 December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, Recent Accounting Pronouncements Not Yet Adopted There are currently no recent accounting pronouncements that have not yet been adopted and that would have a material effect, once adopted, on the condensed consolidated financial statements.

Cash, Cash Equivalents and Rest

Cash, Cash Equivalents and Restricted Cash	6 Months Ended
	Jun. 30, 2021
Cash And Cash Equivalents [Abstract]
Cash, Cash Equivalents and Restricted Cash	2. CASH, CASH EQUIVALENTS AND RESTRICTED CASH The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Condensed Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Condensed Consolidated Statements of Cash Flows: As of As of (In thousands) June 30, 2021 December 31, 2020 Cash and cash equivalents $ 69,927 $ 60,161 Restricted cash 54 18 Cash, cash equivalents and restricted cash $ 69,981 $ 60,179 See Note 18 for additional information regarding restricted cash.

Revenue

Revenue	6 Months Ended
	Jun. 30, 2021
Revenue From Contract With Customer [Abstract]
Revenue	3. REVENUE The following is a description of the principal activities from which revenue is generated by reportable segment: 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. Services & Support Segment - Includes maintenance, network implementation, solutions integration and managed services, which include hosted cloud services and subscription services. Revenue by Category In addition to our reportable segments, revenue is also reported for the following three categories – Access & Aggregation, Subscriber Solutions & Experience and Traditional & Other Products. The following tables disaggregate revenue by reportable segment and revenue category: Three Months Ended June 30, 2021 June 30, 2020 (In thousands) Network Solutions Services & Support Total Network Solutions Services & Support Total Access & Aggregation $ 78,307 $ 12,657 $ 90,964 $ 69,721 $ 13,055 $ 82,776 Subscriber Solutions & Experience 45,097 2,713 47,810 38,081 2,312 40,393 Traditional & Other Products 2,045 2,413 4,458 3,521 2,025 5,546 Total $ 125,449 $ 17,783 $ 143,232 $ 111,323 $ 17,392 $ 128,715 Six Months Ended June 30, 2021 June 30, 2020 (In thousands) Network Solutions Services & Support Total Network Solutions Services & Support Total Access & Aggregation $ 138,360 $ 21,678 $ 160,038 $ 122,776 $ 25,966 $ 148,742 Subscriber Solutions & Experience 97,366 5,013 102,379 78,064 4,508 82,572 Traditional & Other Products 3,532 4,816 8,348 7,855 4,069 11,924 Total $ 239,258 $ 31,507 $ 270,765 $ 208,695 $ 34,543 $ 243,238 Revenue allocated to remaining performance obligations represents contract revenues that have not yet been recognized for contracts with a duration of greater than one year. As of June 30, 2021, 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 that we are entitled to invoice, which correspond to the value of completed performance obligations to date. The amount related to these performance obligations was $19.7 million and $17.7 million as of June 30, 2021 and December 31, 2020, respectively. The Company expects to recognize 64% of the $19.7 million as of June 30, 2021 over the next 12 months, with the remainder to be recognized thereafter. The following table provides information about receivables, contract assets and unearned revenue from contracts with customers: As of As of (In thousands) June 30, 2021 December 31, 2020 Accounts receivable, net $ 122,669 $ 98,827 Contract assets (1) $ 1,036 $ 63 Unearned revenue $ 15,889 $ 14,092 Non-current unearned revenue $ 7,030 $ 6,888 (1) Included in other receivables on the Condensed Consolidated Balance Sheets. Of the outstanding unearned revenue balances as of December 31, 2020 $2.9 million and $7.9 million were recognized as revenue during the three and six months ended June 30, 2021, respectively.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	4. INCOME TAXES Our effective tax rate decreased from an expense of 68.5% for the three months ended June 30, 2020, to an expense of 18.1% for the three months ended June 30, 2021 and The change in the effective tax rate for the three months ended June 30, 2021 was driven by tax expense in our international operations and additional changes in the valuation allowance related to our domestic operations. 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 June 30, 2021, the Company had deferred tax assets totaling $ 56.9 million, and a valuation allowance totaling $ 47.8 million against those deferred tax assets. The remaining $ 9.2 million in deferred tax assets 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. Our assessment of the realizability of our deferred tax assets includes the evaluation of historical operating results as well as the evaluation of evidence which requires significant judgement, including the evaluation of our three-year cumulative income position, future taxable income projections and tax planning strategies. Should management’s conclusion change in the future and an additional valuation allowance or a partial or full release of the valuation allowance becomes necessary, it could have a material effect on our consolidated financial statements. Supplemental balance sheet information related to deferred tax assets is as follows: As of June 30, 2021 (In thousands) Deferred Tax Assets Valuation Allowance Deferred Tax Assets, net Domestic $ 45,383 $ (45,383 ) $ — International 11,558 (2,393 ) 9,165 Total $ 56,941 $ (47,776 ) $ 9,165 As of 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

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	5. STOCK-BASED COMPENSATION The following table summarizes stock-based compensation expense related to stock options, performance stock units (“PSUs”), restricted stock units (“RSUs”) and restricted stock: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Stock-based compensation expense included in cost of revenue $ 125 $ 87 $ 256 $ 202 Selling, general and administrative expense 1,098 971 2,196 2,046 Research and development expense 585 597 1,163 1,198 Stock-based compensation expense included in operating expenses 1,683 1,568 3,359 3,244 Total stock-based compensation expense 1,808 1,655 3,615 3,446 Tax benefit for expense associated with stock options, PSUs, RSUs and restricted stock (452 ) (394 ) (883 ) (821 ) Total stock-based compensation expense, net of tax $ 1,356 $ 1,261 $ 2,732 $ 2,625 PSUs, RSUs and Restricted Stock The following table summarizes PSUs, RSUs and restricted stock outstanding as of December 31, 2020 and June 30, 2021 and the changes that occurred during the six months ended June 30, 2021: Number of Shares (in thousands) Weighted Avg. Grant Date Fair Value (per share) Unvested PSUs, RSUs and restricted stock outstanding, December 31, 2020 1,846 $ 11.49 PSUs, RSUs and restricted stock granted 357 $ 16.73 PSUs, RSUs and restricted stock vested (12 ) $ 11.76 PSUs, RSUs and restricted stock forfeited (47 ) $ 11.58 Unvested PSUs, RSUs and restricted stock outstanding, June 30, 2021 2,144 $ 12.41 During each of the six month periods ended June 30, 2021 and 2020, the Company granted 0.3 million performance-based PSUs to its executive officers and certain employees. The grant-date fair value of these performance-based awards was based on the closing price of the Company’s stock on the date of grant. These awards vest over two-year three-year the achievement of defined performance targets. Equity-based compensation expense with respect to these awards may be adjusted over the vesting period to reflect the probability of achievement of performance targets defined in the award agreements. The fair value of RSUs and restricted stock is equal to the closing price of our stock on the date of grant. The fair value of PSUs with market conditions is calculated using a Monte Carlo simulation valuation method. As of June 30, 2021, total unrecognized compensation expense related to non-vested market-based PSUs, RSUs and restricted stock was approximately $13.2 million, which will be recognized over the remaining weighted-average period of 2.5 years. In addition, there was $7.5 million of unrecognized compensation expense related to unvested 2020 and 2021 performance-based PSUs, which will be recognized over the remaining requisite service period of 1.5 years if achievement of the performance obligation becomes probable. Unrecognized compensation expense will be adjusted for actual forfeitures. As of June 30, 2021, 3.5 million shares were available for issuance under stockholder-approved equity plans. Stock Options The following table summarizes stock options outstanding as of December 31, 2020 and June 30, 2021 and the changes that occurred during the six months ended June 30, 2021: Number of Stock Options (in thousands) Weighted Avg. Exercise Price (per share) Weighted Avg. Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Stock options outstanding, December 31, 2020 2,718 $ 21.17 2.9 $ — Stock options exercised (215 ) $ 16.53 588 Stock options expired (117 ) $ 23.37 17 Stock options outstanding, June 30, 2021 2,386 $ 21.47 2.4 $ 4,721 Stock options exercisable, June 30, 2021 2,386 $ 21.47 2.4 $ 4,721 As of June 30, 2021, there was no unrecognized compensation expense related to stock options as all awards vested in prior periods. There were no stock options granted during the six months ended June 30, 2021 or 2020. All of the options were previously issued at exercise prices that approximated fair market value at the date of grant. The aggregate intrinsic value of stock options represents the total pre-tax intrinsic value (the difference between ADTRAN’s closing stock price on the last trading day of the quarter 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 June 30, 2021. The amount of aggregate intrinsic value was $4.7 million as of June 30, 2021 and will change based on the fair market value of ADTRAN’s stock. The total pre-tax intrinsic value of options exercised during the six months ended June 30, 2021 was $0.6 million.

Investments

Investments	6 Months Ended
	Jun. 30, 2021
Investments Debt And Equity Securities [Abstract]
Investments	6. INVESTMENTS Debt Securities and Other Investments The following debt securities and other investments were included on the Condensed Consolidated Balance Sheet and recorded at fair value: As of June 30, 2021 Amortized Gross Unrealized Fair (In thousands) Cost Gains Losses Value Corporate bonds $ 14,954 $ 53 $ (6 ) $ 15,001 Municipal fixed-rate bonds 2,523 15 (1 ) 2,537 Asset-backed bonds 3,983 20 (2 ) 4,001 Mortgage/Agency-backed bonds 11,004 50 (15 ) 11,039 U.S. government bonds 10,777 51 (5 ) 10,823 Foreign government bonds 546 1 (1 ) 546 Other 533 — — 533 Available-for-sale debt securities held at fair value $ 44,320 $ 190 $ (30 ) $ 44,480 As of December 31, 2020 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 The contractual maturities related to debt securities and other investments were as follows: As of June 30, 2021 (In thousands) Corporate bonds Municipal fixed-rate bonds Asset- backed bonds Mortgage/ Agency- backed bonds U.S. government bonds Foreign government bonds Other Less than one year $ 436 $ 529 $ 1 $ 254 $ 735 $ — $ 533 One to two years 4,575 496 — 1,865 7,240 — — Two to three years 7,518 1,103 50 1,199 1,188 546 — Three to five years 2,472 409 1,749 165 1,660 — — Five to ten years — — 866 2,213 — — — More than ten years — — 1,335 5,343 — — — Total $ 15,001 $ 2,537 $ 4,001 $ 11,039 $ 10,823 $ 546 $ 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 debt securities are computed under the specific identification method. The following table presents the gross realized gains and losses related to our debt securities: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Gross realized gain on debt securities $ 97 $ 190 $ 184 $ 233 Gross realized loss on debt securities (20 ) (19 ) (36 ) (39 ) Total gain recognized, net $ 77 $ 171 $ 148 $ 194 No allowance for credit loss was recorded for the six months ended June 30, 2021 or 2020 related to available-for-sale debt securities. 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 our total investment portfolio. The Company did not purchase any available-for-sale debt security with credit deterioration during the six months ended June 30, 2021. Marketable Equity Securities Our marketable equity securities consist of publicly traded stock, interests in funds and certain other investments measured at fair value or cost (where appropriate). In March 2019, an outstanding note receivable of $4.3 million owed to the Company 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. The Company elected to record this equity investment that does not have a readily determinable fair value 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. During the year ended December 31, 2020, impairment charges totaling $2.6 million were recorded related to this equity investment, which was included in net investment gain (loss) on the Condensed Consolidated Statement of Income (Loss). As a result the carrying value of this investment was $0.8 million as of June 30, 2021 and 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 Condensed Consolidated Balance Sheets as of June 30, 2021 and December 31, 2020. No impairment charge was recognized related to the note receivable as it is a secured loan. Realized and unrealized gains and losses related to marketable equity securities were as follows: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Realized gain (loss) on equity securities sold $ (79 ) $ 328 $ (55 ) $ (2,108 ) Unrealized gain on equity securities held 2,011 9,353 2,912 889 Total gain (loss) recognized, net $ 1,932 $ 9,681 $ 2,857 $ (1,219 ) U.S. GAAP establishes a three-level valuation hierarchy based upon observable and unobservable inputs for fair value measurement of financial instruments: • 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. The Company’s cash equivalents and investments held at fair value are categorized into this hierarchy as follows: Fair Value Measurements as of June 30, 2021 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 $ 615 $ 615 $ — $ — Commercial paper 1,250 — 1,250 — Available-for-sale debt securities Corporate bonds 15,001 — 15,001 — Municipal fixed-rate bonds 2,537 — 2,537 — Asset-backed bonds 4,001 — 4,001 — Mortgage/Agency-backed bonds 11,039 — 11,039 — U.S. government bonds 10,823 10,823 — — Foreign government securities 546 — 546 — Other 533 — — 533 Marketable equity securities Marketable equity securities – various industries 12,057 12,057 — — Deferred compensation plan assets 25,917 25,917 — — Other investments 1,400 1,400 — — Total $ 85,719 $ 50,812 $ 34,374 $ 533 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 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 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 consists of third-party valuations performed in accordance with ASC 820 – Fair Value Measurement.

Inventory

Inventory	6 Months Ended
	Jun. 30, 2021
Inventory Disclosure [Abstract]
Inventory	7. INVENTORY Inventory consisted of the following: As of As of (In thousands) June 30, 2021 December 31, 2020 Raw materials $ 52,257 $ 47,026 Work in process 1,874 776 Finished goods 64,881 77,655 Total inventory, net $ 119,012 $ 125,457 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 June 30, 2021 and December 31, 2020, inventory reserves were $42.7 million and $39.6 million, respectively

Property, Plant and Equipment

Property, Plant and Equipment	6 Months Ended
	Jun. 30, 2021
Property Plant And Equipment [Abstract]
Property, Plant and Equipment	8. PROPERTY, PLANT AND EQUIPMENT Property, plant and equipment consisted of the following: As of As of (In thousands) June 30, 2021 December 31, 2020 Land $ 4,575 $ 4,575 Building and land improvements 34,961 35,142 Building 68,161 68,169 Furniture and fixtures 19,936 19,965 Computer hardware and software 71,262 70,942 Engineering and other equipment 134,090 132,920 Total property, plant and equipment 332,985 331,713 Less: accumulated depreciation $ (274,715 ) $ (269,314 ) Total property, plant and equipment, net $ 58,270 $ 62,399 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. Due to the current economic environment, particularly related to COVID-19, the Company assessed impairment triggers related to long-lived assets during the second quarters of 2021 and 2020. Based on this assessment, no triggers occurred to perform an impairment test, and no impairment losses of long-lived assets were recorded for the three or six months ended June 30, 2021 or 2020 Depreciation expense was $3.0 million for each of the three months ended June 30, 2021 and 2020 and $6.1 million and $6.0 million for the six months ended June 30, 2021 and 2020, respectively, which is recorded in cost of revenue, selling, general and administrative expenses and research and development expenses in the Condensed Consolidated Statements of Income (Loss).

Goodwill

Goodwill	6 Months Ended
	Jun. 30, 2021
Goodwill Disclosure [Abstract]
Goodwill	9. GOODWILL Goodwill was $7.0 million as of June 30, 2021 and December 31, 2020, 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 assess qualitative factors to determine whether the fair value of the reporting unit to which the goodwill is assigned is less than its carrying amount and recognize an impairment charge for the amount by which the carrying value exceeds the fair value of the reporting unit. Due to the current economic environment, particularly related to COVID-19, the Company performed a triggering event assessment during the second quarters of 2021 and 2020, in which no triggers were identified. Therefore, no interim impairment test of goodwill was performed

Intangible Assets

Intangible Assets	6 Months Ended
	Jun. 30, 2021
Intangible Assets Net Excluding Goodwill [Abstract]
Intangible Assets	10. Intangible assets consisted of the following: As of June 30, 2021 As of December 31, 2020 (In thousands) Gross Carrying Amount Accumulated Amortization Net Book Value Gross Carrying Amount Accumulated Amortization Net Book Value Customer relationships $ 20,985 $ (9,030 ) $ 11,955 $ 21,123 $ (8,055 ) $ 13,068 Developed technology 8,200 (3,114 ) 5,086 8,200 (2,546 ) 5,654 Licensed technology 5,900 (2,158 ) 3,742 5,900 (1,830 ) 4,070 Supplier relationships — — — 2,800 (2,800 ) — Licensing agreements 560 (189 ) 371 560 (152 ) 408 Patents 500 (329 ) 171 500 (294 ) 206 Trade names 210 (181 ) 29 210 (146 ) 64 Total $ 36,355 $ (15,001 ) $ 21,354 $ 39,293 $ (15,823 ) $ 23,470 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. Due to the current economic environment, particularly related to COVID-19, the Company assessed impairment triggers related to intangible assets during the second quarters of 2021 and 2020. Based on this assessment, no triggers occurred that required us to perform an impairment test, and no impairment losses of intangible assets were recorded for the three and six months ended June 30, 2021 or 2020. Amortization expense was $1.0 million in each of the three months ended June 30, 2021 and 2020 and $2.1 million and $2.4 million for the six months ended June 30, 2021 and 2020, respectively, and was included in cost of revenue, selling, general and administrative expenses and research and development expenses Estimated future amortization expense of intangible assets was as follows: As of (In thousands) June 30, 2021 2021 $ 2,028 2022 3,485 2023 3,333 2024 3,238 2025 3,029 Thereafter 6,241 Total $ 21,354

Leases

Leases	6 Months Ended
	Jun. 30, 2021
Leases [Abstract]
Leases	11. LEASES Net Investment in Sales-Type Leases We are the lessor in sales-type lease arrangements for network equipment, which consisted of the following: As of As of (In thousands) June 30, 2021 December 31, 2020 Current minimum lease payments receivable (1) $ 103 $ 702 Non-current minimum lease payments receivable (2) 13 347 Total minimum lease payments receivable 116 1,049 Less: Current unearned revenue 60 218 Less: Non-current unearned revenue 2 50 Net investment in sales-type leases $ 54 $ 781 (1) Included in other receivables on the Condensed Consolidated Balance Sheets. (2) Included in other assets on the Condensed Consolidated Balance Sheets.

Revolving Credit Agreement

Revolving Credit Agreement	6 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Revolving Credit Agreement	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 June 30, 2021.

Alabama State Industrial Develo

Alabama State Industrial Development Authority Financing and Economic Incentives	6 Months Ended
	Jun. 30, 2021
Text Block [Abstract]
Alabama State Industrial Development Authority Financing and Economic Incentives	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 to $50.0 million. The Taxable Revenue Bonds bore interest, payable monthly with an interest rate of 2% per annum. The Taxable Revenue Bonds aggregate principal amount of $24.6 million matured on January 1, 2020 and was repaid in full on January 2, 2020, using the funds held in a certificate of deposit by the Company.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Stockholders' Equity	14. STOCKHOLDERS’ EQUITY Stock Repurchase Program Since 1997, the Company’s Board of Directors has approved multiple share repurchase programs that have authorized repurchases of its common stock, which are implemented through open market or private purchases from time to time as conditions warrant. During the six months ended June 30, 2021, we did not repurchase any shares of our common stock. As of June 30, 2021, we had the authority to purchase an additional 2.5 million shares of our common stock under the current authorization of up to 5.0 million shares. Accumulated Other Comprehensive Income (Loss) The following tables present the changes in accumulated other comprehensive loss, net of tax, by component: Three Months Ended June 30, 2021 (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption Total As of March 31, 2021 $ (160 ) $ (9,522 ) $ (4,298 ) $ 385 $ (13,595 ) Other comprehensive income before reclassifications (272 ) — 338 — 66 Amounts reclassified from accumulated other comprehensive income 177 212 — — 389 Net current period other comprehensive income (95 ) 212 338 — 455 As of June 30, 2021 $ (255 ) $ (9,310 ) $ (3,960 ) $ 385 $ (13,140 ) Three Months Ended June 30, 2020 (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption Total As of March 31, 2020 $ (167 ) $ (9,085 ) $ (8,942 ) $ 385 $ (17,809 ) Other comprehensive income before reclassifications 881 — 1,899 — 2,780 Amounts reclassified from accumulated other comprehensive income (loss) (508 ) 191 — — (317 ) Net current period other comprehensive income 373 191 1,899 — 2,463 As of June 30, 2020 $ 206 $ (8,894 ) $ (7,043 ) $ 385 $ (15,346 ) Six Months Ended June 30, 2021 (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption Total As of December 31, 2020 $ 32 $ (9,621 ) $ (2,435 ) $ 385 $ (11,639 ) Other comprehensive income (loss) before reclassifications (329 ) — (1,525 ) — (1,854 ) Amounts reclassified from accumulated other comprehensive income 42 311 — — 353 Net current period other comprehensive income (loss) (287 ) 311 (1,525 ) — (1,501 ) As of June 30, 2021 $ (255 ) $ (9,310 ) $ (3,960 ) $ 385 $ (13,140 ) Six Months Ended June 30, 2020 (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption Total As of December 31, 2019 $ (284 ) $ (9,226 ) $ (7,292 ) $ 385 $ (16,417 ) Other comprehensive income (loss) before reclassifications (50 ) — 249 — 199 Amounts reclassified from accumulated other comprehensive income (loss) 540 332 — — 872 Amounts reclassified to retained earnings — — — — — Net current period other comprehensive income (loss) 490 332 249 — 1,071 As of June 30, 2020 $ 206 $ (8,894 ) $ (7,043 ) $ 385 $ (15,346 ) The following tables present the details of reclassifications out of accumulated other comprehensive income (loss): Three Months Ended June 30, 2021 (In thousands) Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Statement Where Net Income Is Presented Unrealized gain (loss) on available-for-sale securities: Net realized loss on sales of securities $ (233 ) Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (307 ) (1) Total reclassifications for the period, before tax (540 ) Tax benefit 151 Total reclassifications for the period, net of tax $ (389 ) (1) A part of the computation of net periodic pension cost, which is included in other income (expense), net in the Condensed Consolidated Statements of Income (Loss). Three Months Ended June 30, 2020 (In thousands) Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Statement Where Net Income Is Presented Unrealized gain (loss) on available-for-sale securities: Net realized gain on sales of securities $ 686 Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (277 ) (1) Total reclassifications for the period, before tax 409 Tax expense (92 ) Total reclassifications for the period, net of tax $ 317 (1) A part of the computation of net periodic pension cost, which is included in other income (expense), net in the Condensed Consolidated Statements of Income (Loss). Six Months Ended June 30, 2021 (In thousands) Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Statement Where Net Income Is Presented Unrealized gain (loss) on available-for-sale securities: Net realized loss on sales of securities $ (55 ) Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (451 ) (1) Total reclassifications for the period, before tax (506 ) Tax benefit 153 Total reclassifications for the period, net of tax $ (353 ) (1) A part of the computation of net periodic pension cost, which is included in other income (expense), net in the Condensed Consolidated Statements of Income (Loss). Six Months Ended June 30, 2020 (In thousands) Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Statement Where Net Income Is Presented Unrealized gain (loss) on available-for-sale securities: Net realized loss on sales of securities $ (730 ) Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (481 ) (1) Total reclassifications for the period, before tax (1,211 ) Tax benefit 339 Total reclassifications for the period, net of tax $ (872 ) (1) A part of the computation of net periodic pension cost, which is included in other income (expense), net in the Condensed Consolidated Statements of Income (Loss). The following tables present the tax effects related to the change in each component of other comprehensive income (loss): Three Months Ended Three Months Ended June 30, 2021 June 30, 2020 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gain (loss) on available-for-sale securities $ (358 ) $ 86 $ (272 ) $ 1,191 $ (310 ) $ 881 Reclassification adjustment for amounts related to available-for-sale investments included in net income (loss) 233 (56 ) 177 (686 ) 178 (508 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income (loss) 307 (95 ) 212 277 (86 ) 191 Foreign currency translation adjustment 338 — 338 1,899 — 1,899 Total Other Comprehensive Income $ 520 $ (65 ) $ 455 $ 2,681 $ (218 ) $ 2,463 Six Months Ended Six Months Ended June 30, 2021 June 30, 2020 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gain (loss) on available-for-sale securities $ (433 ) $ 104 $ (329 ) $ (68 ) $ 18 $ (50 ) Reclassification adjustment for amounts related to available-for-sale investments included in net income 55 (13 ) 42 730 (190 ) 540 Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income 451 (140 ) 311 481 (149 ) 332 Foreign currency translation adjustment (1,525 ) — (1,525 ) 249 — 249 Total Other Comprehensive Income (Loss) $ (1,452 ) $ (49 ) $ (1,501 ) $ 1,392 $ (321 ) $ 1,071

Earnings (Loss) Per Share

Earnings (Loss) Per Share	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Earnings (Loss) Per Share	15. EARNINGS (LOSS) PER SHARE The calculation of basic and diluted earnings (loss) per share is as follows: Three Months Ended Six Months Ended June 30, June 30, (In thousands, except per share amounts) 2021 2020 2021 2020 Numerator Net income (loss) $ 5,086 $ 752 $ 5,982 $ (9,217 ) Denominator Weighted average number of shares – basic 48,449 47,958 48,393 47,957 Effect of dilutive securities PSUs, RSUs and restricted stock 816 296 722 — Stock options 161 — 110 — Weighted average number of shares – diluted 49,426 48,254 49,225 47,957 Earnings (loss) per share – basic $ 0.10 $ 0.02 $ 0.12 $ (0.19 ) Earnings (loss) per share – diluted $ 0.10 $ 0.02 $ 0.12 $ (0.19 ) For the three months ended June 30, 2021 and 2020, 0.4 million and 1.9 million stock options, respectively, and for the six months ended June 30, 2021 and 2020, 0.6 million and 2.3 million stock options, respectively, were outstanding but were not included in the computation of diluted earnings per share. These stock options were excluded because their exercise prices were greater than the average market price of the common shares during the applicable period, making them anti-dilutive under the treasury stock method. For the three months ended June 30, 2021 and 2020 , one thousand and fifteen thousand shares, respectively, and for the six months ended June 30, 2021 and 2020 , three thousand and 0.1 million shares, respectively, of unvested PSUs, RSUs and restricted stock were excluded from the calculation of diluted earnings per share due to their anti-dilutive effect.

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Segment Information	16. SEGMENT INFORMATION 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 and software products and 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 installation and solution integration services, which include hosted cloud services and subscription services. The performance of these segments 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), net and income tax benefit (expense) 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 tables present information about the revenue and gross profit of our reportable segments: Three Months Ended June 30, 2021 June 30, 2020 (In thousands) Revenue Gross Profit Revenue Gross Profit Network Solutions $ 125,449 $ 55,435 $ 111,323 $ 47,252 Services & Support 17,783 7,233 17,392 6,220 Total $ 143,232 $ 62,668 $ 128,715 $ 53,472 Six Months Ended June 30, 2021 June 30, 2020 (In thousands) Revenue Gross Profit Revenue Gross Profit Network Solutions $ 239,258 $ 104,243 $ 208,695 $ 92,998 Services & Support 31,507 12,026 34,543 12,074 Total $ 270,765 $ 116,269 $ 243,238 $ 105,072 Revenue by Category In addition to our reportable segments, revenue is also reported for the following three categories – Access & Aggregation, Subscriber Solutions & Experience and Traditional & Other Products. The table below presents revenue information by category: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Access & Aggregation $ 90,964 $ 82,776 $ 160,038 $ 148,742 Subscriber Solutions & Experience 47,810 40,393 102,379 82,572 Traditional & Other Products 4,458 5,546 8,348 11,924 Total $ 143,232 $ 128,715 $ 270,765 $ 243,238 Revenue by Geographic Area The following table presents revenue information by geographic area: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 United States $ 94,656 $ 84,458 $ 181,141 $ 163,449 International 48,576 44,257 89,624 79,789 Total $ 143,232 $ 128,715 $ 270,765 $ 243,238

Liability for Warranty Returns

Liability for Warranty Returns	6 Months Ended
	Jun. 30, 2021
Product Warranties Disclosures [Abstract]
Liability for Warranty Returns	17. LIABILITY FOR WARRANTY RETURNS 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 may cause warranty incidences, when they arise, to be more costly. 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 $6.0 million and $7.1 million as of June 30, 2021 and December 31, 2020, respectively, and is included in accrued expenses and other liabilities in the Condensed Consolidated Balance Sheets. During the three and six months ended June 30, 2021 and 2020, we had a reversal of prior provisions related to warranty expirations, the impact of which is reflected in the table below: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Balance at beginning of period $ 6,472 $ 7,635 $ 7,146 $ 8,394 Plus: Amounts charged to cost and expenses 11 393 (220 ) 338 Less: Deductions (486 ) (734 ) (929 ) (1,438 ) Balance at end of period $ 5,997 $ 7,294 $ 5,997 $ 7,294

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	18. COMMITMENTS AND CONTINGENCIES Shareholder Derivative Lawsuit On March 31, 2020, a shareholder derivative suit, captioned Johnson (Derivatively on behalf of ADTRAN) v. Stanton, et al., Case No. 5:20-cv-00447, was filed in the U.S. District Court for the Northern District of Alabama against two of the Company’s current executive officers, one of its former executive officers, and certain current and former members of its Board of Directors. The derivative suit alleges, among other things, that the defendants made or caused the Company to make 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 case was temporarily stayed pending an order on the defendants’ motion to dismiss in a separate securities class action case that included similar factual allegations, Burbridge v. ADTRAN, Inc., et al., Case No. 5:20-cv-00050-LCB (N.D. Ala.). The Burbridge case was dismissed on March 31, 2021, and the time to appeal the dismissal has expired, such that the dismissal is now final. Following the dismissal, the plaintiff in the shareholder derivative suit sent a demand letter dated June 29, 2021 to ADTRAN’s Board of Directors. The letter contains similar allegations to those made in the plaintiff’s filed complaint and in the now dismissed securities class action, and it demands, among other things, that the Board commence an investigation into the alleged wrongdoing. We expect that the derivative suit will remain stayed pending the Board’s response to the demand. At this time, we are unable to predict the outcome of or estimate the possible loss or range of loss, if any, associated with the derivative lawsuit or the demand letter. 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 patent rights, employment matters, 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 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 June 30, 2021 and December 31, 2020, we had commitments related to these bonds totaling $21.2 million and $15.2 million, respectively, which expire at various dates through August 2024. 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. We reached the maximum value of our minimum collateral requirement of $ 15.0 million during the three months ended March 31, 2021 as the Company reached certain milestones through the first quarter of 2021 as outlined in the customer contract. The letter of credit was secured by a pledge of a portion of the Company’s fixed-income securities, which totaled $18.2 million as of June 30, 2021, of which less than $0.1 million is included in restricted cash and $18.2 million is included in long-term investments on the Condensed Consolidated Balance Sheet. This pledged collateral value will fluctuate as the Company changes the mix of the pledged collateral between restricted cash and investments. Any shortfalls in the minimum collateral value are required to be restored by the Company from available cash and cash equivalents, short-term investments and/or long-term investments. The collateral under the letter of credit will be released when all obligations under the customer contract have been met. As of June 30, 2021, the Company was in compliance with all contractual requirements under the letter of credit. 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 invested as of June 30, 2021.

Restructuring

Restructuring	6 Months Ended
	Jun. 30, 2021
Restructuring And Related Activities [Abstract]
Restructuring	19. 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 the first half of 2021 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 June 30, 2021 for the restructuring plans was $12.5 million. A reconciliation of the beginning and ending restructuring liability, which is included in accrued wages and benefits in the Condensed Consolidated Balance Sheets is as follows: Three Months Ended Six Months Ended (In thousands) June 30, 2021 June 30, 2021 Balance at beginning of period $ 2,077 $ 4,186 Plus: Amounts charged to cost and expense 8 309 Less: Amounts paid (565 ) (2,975 ) Balance as of June 30, 2021 $ 1,520 $ 1,520 (In thousands) For the Year Ended December 31, 2020 Balance as of December 31, 2019 $ 1,568 Plus: Amounts charged to cost and expense 6,229 Less: Amounts paid (3,611 ) Balance as of December 31, 2020 $ 4,186 Restructuring expenses included in the Condensed Consolidated Statements of Income (Loss) were as follows: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Cost of revenue $ - $ 22 $ 15 $ 56 Selling, general and administrative expenses 3 489 145 572 Research and development expenses 5 681 149 1,117 Total restructuring expenses $ 8 $ 1,192 $ 309 $ 1,745 Components of restructuring expense by geographic area were as follows: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 United States $ 3 $ 1,192 $ 212 $ 1,743 International 5 — 97 2 Total restructuring expenses $ 8 $ 1,192 $ 309 $ 1,745

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	20. SUBSEQUENT EVENTS On August 4, 2021, we announced that our Board of Directors declared a quarterly cash dividend of $0.09 per common share to be paid to the Company’s stockholders of record as of the close of business on August 19, 2021. The payment date will be September 2, 2021 in the aggregate amount of approximately $4.4 million.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements of ADTRAN ® In the opinion of management, all adjustments necessary to fairly state these interim statements have been recorded and are of a normal and recurring nature. The results of operations for an interim period are not necessarily indicative of the results for the full year. The interim financial statements should be read in conjunction with the consolidated financial statements and notes thereto included in ADTRAN’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on February 26, 2021.
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 expense during the reporting period. The more significant estimates include excess and obsolete inventory reserves, warranty reserves, customer rebates, determination and accrual of deferred revenue components of multi-element sales agreements, estimated costs to complete obligations associated with deferred and accrued 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 and fair value of investments. 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 SARS-CoV-2 coronavirus/COVID-19 global pandemic (or variants of the SARS-CoV-2 coronavirus, including the Delta variant) as of June 30, 2021 and through the date of this report. The accounting matters assessed included, but were not limited to, the allowance for expected credit losses, stock-based compensation, 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 six months ended June 30, 2021 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 an Immaterial Misstatement	Correction of an Immaterial Misstatement During the three months ended March 31, 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 l ong-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 by remeasuring the investment assets to their historical cost basis through the recording of a n et investment gain of $ 1.5 million in the unaudited Condensed Consolidated Statement of Income (Loss) and then correcting the classification by decreasing the l ong-term investment balance at its remeasured cost basis of $ 2.8 million to Treasury stock in the unaudited Condensed Consolidated Balance Sheet as of March 31, 2020. Management has determined that this misstatement was not material to any of its previously issued financial statements and that the correction of the misstatement was not material to the Company’s 2020 annual financial results on either a quantitative or qualitative basis.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements We recently adopted the following accounting standards, which had the following impacts on our condensed consolidated financial statements: 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 December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes,
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted There are currently no recent accounting pronouncements that have not yet been adopted and that would have a material effect, once adopted, on the condensed consolidated financial statements.

Cash, Cash Equivalents and Re_2

Cash, Cash Equivalents and Restricted Cash (Tables)	6 Months Ended
	Jun. 30, 2021
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 Condensed Consolidated Balance Sheets that sum to the total of the same such amounts shown in the Condensed Consolidated Statements of Cash Flows: As of As of (In thousands) June 30, 2021 December 31, 2020 Cash and cash equivalents $ 69,927 $ 60,161 Restricted cash 54 18 Cash, cash equivalents and restricted cash $ 69,981 $ 60,179

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2021
Revenue From Contract With Customer [Abstract]
Disaggregate of Revenue by Reportable Segment and Revenue Category	The following tables disaggregate revenue by reportable segment and revenue category: Three Months Ended June 30, 2021 June 30, 2020 (In thousands) Network Solutions Services & Support Total Network Solutions Services & Support Total Access & Aggregation $ 78,307 $ 12,657 $ 90,964 $ 69,721 $ 13,055 $ 82,776 Subscriber Solutions & Experience 45,097 2,713 47,810 38,081 2,312 40,393 Traditional & Other Products 2,045 2,413 4,458 3,521 2,025 5,546 Total $ 125,449 $ 17,783 $ 143,232 $ 111,323 $ 17,392 $ 128,715 Six Months Ended June 30, 2021 June 30, 2020 (In thousands) Network Solutions Services & Support Total Network Solutions Services & Support Total Access & Aggregation $ 138,360 $ 21,678 $ 160,038 $ 122,776 $ 25,966 $ 148,742 Subscriber Solutions & Experience 97,366 5,013 102,379 78,064 4,508 82,572 Traditional & Other Products 3,532 4,816 8,348 7,855 4,069 11,924 Total $ 239,258 $ 31,507 $ 270,765 $ 208,695 $ 34,543 $ 243,238 The table below presents revenue information by category: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Access & Aggregation $ 90,964 $ 82,776 $ 160,038 $ 148,742 Subscriber Solutions & Experience 47,810 40,393 102,379 82,572 Traditional & Other Products 4,458 5,546 8,348 11,924 Total $ 143,232 $ 128,715 $ 270,765 $ 243,238
Information about Receivables, Contract Assets, and Unearned Revenue from Contracts with Customers	The following table provides information about receivables, contract assets and unearned revenue from contracts with customers: As of As of (In thousands) June 30, 2021 December 31, 2020 Accounts receivable, net $ 122,669 $ 98,827 Contract assets (1) $ 1,036 $ 63 Unearned revenue $ 15,889 $ 14,092 Non-current unearned revenue $ 7,030 $ 6,888 (1) Included in other receivables on the Condensed Consolidated Balance Sheets.

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Summary of Supplemental Balance Sheet Information Related to Deferred Tax Assets	Supplemental balance sheet information related to deferred tax assets is as follows: As of June 30, 2021 (In thousands) Deferred Tax Assets Valuation Allowance Deferred Tax Assets, net Domestic $ 45,383 $ (45,383 ) $ — International 11,558 (2,393 ) 9,165 Total $ 56,941 $ (47,776 ) $ 9,165 As of 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

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
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, performance stock units (“PSUs”), restricted stock units (“RSUs”) and restricted stock: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Stock-based compensation expense included in cost of revenue $ 125 $ 87 $ 256 $ 202 Selling, general and administrative expense 1,098 971 2,196 2,046 Research and development expense 585 597 1,163 1,198 Stock-based compensation expense included in operating expenses 1,683 1,568 3,359 3,244 Total stock-based compensation expense 1,808 1,655 3,615 3,446 Tax benefit for expense associated with stock options, PSUs, RSUs and restricted stock (452 ) (394 ) (883 ) (821 ) Total stock-based compensation expense, net of tax $ 1,356 $ 1,261 $ 2,732 $ 2,625
Summary of PSUs, RSUs and Restricted Stock Outstanding	The following table summarizes PSUs, RSUs and restricted stock outstanding as of December 31, 2020 and June 30, 2021 and the changes that occurred during the six months ended June 30, 2021: Number of Shares (in thousands) Weighted Avg. Grant Date Fair Value (per share) Unvested PSUs, RSUs and restricted stock outstanding, December 31, 2020 1,846 $ 11.49 PSUs, RSUs and restricted stock granted 357 $ 16.73 PSUs, RSUs and restricted stock vested (12 ) $ 11.76 PSUs, RSUs and restricted stock forfeited (47 ) $ 11.58 Unvested PSUs, RSUs and restricted stock outstanding, June 30, 2021 2,144 $ 12.41
Summary of Stock Options Outstanding	The following table summarizes stock options outstanding as of December 31, 2020 and June 30, 2021 and the changes that occurred during the six months ended June 30, 2021: Number of Stock Options (in thousands) Weighted Avg. Exercise Price (per share) Weighted Avg. Remaining Contractual Life (in years) Aggregate Intrinsic Value (in thousands) Stock options outstanding, December 31, 2020 2,718 $ 21.17 2.9 $ — Stock options exercised (215 ) $ 16.53 588 Stock options expired (117 ) $ 23.37 17 Stock options outstanding, June 30, 2021 2,386 $ 21.47 2.4 $ 4,721 Stock options exercisable, June 30, 2021 2,386 $ 21.47 2.4 $ 4,721

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2021
Investments Debt And Equity Securities [Abstract]
Debt Securities and Other Investments, Included on Condensed Consolidated Balance Sheet and Recorded at Fair Value	Debt Securities and Other Investments The following debt securities and other investments were included on the Condensed Consolidated Balance Sheet and recorded at fair value: As of June 30, 2021 Amortized Gross Unrealized Fair (In thousands) Cost Gains Losses Value Corporate bonds $ 14,954 $ 53 $ (6 ) $ 15,001 Municipal fixed-rate bonds 2,523 15 (1 ) 2,537 Asset-backed bonds 3,983 20 (2 ) 4,001 Mortgage/Agency-backed bonds 11,004 50 (15 ) 11,039 U.S. government bonds 10,777 51 (5 ) 10,823 Foreign government bonds 546 1 (1 ) 546 Other 533 — — 533 Available-for-sale debt securities held at fair value $ 44,320 $ 190 $ (30 ) $ 44,480 As of December 31, 2020 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
Contractual Maturities of Debt Securities and Other Investments	The contractual maturities related to debt securities and other investments were as follows: As of June 30, 2021 (In thousands) Corporate bonds Municipal fixed-rate bonds Asset- backed bonds Mortgage/ Agency- backed bonds U.S. government bonds Foreign government bonds Other Less than one year $ 436 $ 529 $ 1 $ 254 $ 735 $ — $ 533 One to two years 4,575 496 — 1,865 7,240 — — Two to three years 7,518 1,103 50 1,199 1,188 546 — Three to five years 2,472 409 1,749 165 1,660 — — Five to ten years — — 866 2,213 — — — More than ten years — — 1,335 5,343 — — — Total $ 15,001 $ 2,537 $ 4,001 $ 11,039 $ 10,823 $ 546 $ 533
Gross Realized Gains and Losses on Sale of Debt Securities	The following table presents the gross realized gains and losses related to our debt securities: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Gross realized gain on debt securities $ 97 $ 190 $ 184 $ 233 Gross realized loss on debt securities (20 ) (19 ) (36 ) (39 ) Total gain recognized, net $ 77 $ 171 $ 148 $ 194
Realized and Unrealized Gains and Losses related to Marketable Equity Securities	Realized and unrealized gains and losses related to marketable equity securities were as follows: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Realized gain (loss) on equity securities sold $ (79 ) $ 328 $ (55 ) $ (2,108 ) Unrealized gain on equity securities held 2,011 9,353 2,912 889 Total gain (loss) recognized, net $ 1,932 $ 9,681 $ 2,857 $ (1,219 )
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 June 30, 2021 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 $ 615 $ 615 $ — $ — Commercial paper 1,250 — 1,250 — Available-for-sale debt securities Corporate bonds 15,001 — 15,001 — Municipal fixed-rate bonds 2,537 — 2,537 — Asset-backed bonds 4,001 — 4,001 — Mortgage/Agency-backed bonds 11,039 — 11,039 — U.S. government bonds 10,823 10,823 — — Foreign government securities 546 — 546 — Other 533 — — 533 Marketable equity securities Marketable equity securities – various industries 12,057 12,057 — — Deferred compensation plan assets 25,917 25,917 — — Other investments 1,400 1,400 — — Total $ 85,719 $ 50,812 $ 34,374 $ 533 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 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

Inventory (Tables)

Inventory (Tables)	6 Months Ended
	Jun. 30, 2021
Inventory Disclosure [Abstract]
Components of Inventory	Inventory consisted of the following: As of As of (In thousands) June 30, 2021 December 31, 2020 Raw materials $ 52,257 $ 47,026 Work in process 1,874 776 Finished goods 64,881 77,655 Total inventory, net $ 119,012 $ 125,457

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	6 Months Ended
	Jun. 30, 2021
Property Plant And Equipment [Abstract]
Property, Plant and Equipment	Property, plant and equipment consisted of the following: As of As of (In thousands) June 30, 2021 December 31, 2020 Land $ 4,575 $ 4,575 Building and land improvements 34,961 35,142 Building 68,161 68,169 Furniture and fixtures 19,936 19,965 Computer hardware and software 71,262 70,942 Engineering and other equipment 134,090 132,920 Total property, plant and equipment 332,985 331,713 Less: accumulated depreciation $ (274,715 ) $ (269,314 ) Total property, plant and equipment, net $ 58,270 $ 62,399

Intangible Assets (Tables)

Intangible Assets (Tables)	6 Months Ended
	Jun. 30, 2021
Intangible Assets Net Excluding Goodwill [Abstract]
Summary of Intangible Assets	Intangible assets consisted of the following: As of June 30, 2021 As of December 31, 2020 (In thousands) Gross Carrying Amount Accumulated Amortization Net Book Value Gross Carrying Amount Accumulated Amortization Net Book Value Customer relationships $ 20,985 $ (9,030 ) $ 11,955 $ 21,123 $ (8,055 ) $ 13,068 Developed technology 8,200 (3,114 ) 5,086 8,200 (2,546 ) 5,654 Licensed technology 5,900 (2,158 ) 3,742 5,900 (1,830 ) 4,070 Supplier relationships — — — 2,800 (2,800 ) — Licensing agreements 560 (189 ) 371 560 (152 ) 408 Patents 500 (329 ) 171 500 (294 ) 206 Trade names 210 (181 ) 29 210 (146 ) 64 Total $ 36,355 $ (15,001 ) $ 21,354 $ 39,293 $ (15,823 ) $ 23,470
Estimated Future Amortization Expense Related to Intangible Assets	Estimated future amortization expense of intangible assets was as follows: As of (In thousands) June 30, 2021 2021 $ 2,028 2022 3,485 2023 3,333 2024 3,238 2025 3,029 Thereafter 6,241 Total $ 21,354

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2021
Leases [Abstract]
Net Investment in Sales-Type Leases	We are the lessor in sales-type lease arrangements for network equipment, which consisted of the following: As of As of (In thousands) June 30, 2021 December 31, 2020 Current minimum lease payments receivable (1) $ 103 $ 702 Non-current minimum lease payments receivable (2) 13 347 Total minimum lease payments receivable 116 1,049 Less: Current unearned revenue 60 218 Less: Non-current unearned revenue 2 50 Net investment in sales-type leases $ 54 $ 781 (1) Included in other receivables on the Condensed Consolidated Balance Sheets. (2) Included in other assets on the Condensed Consolidated Balance Sheets.

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Changes in Accumulated Other Comprehensive Loss, Net of Tax by Component	The following tables present the changes in accumulated other comprehensive loss, net of tax, by component: Three Months Ended June 30, 2021 (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption Total As of March 31, 2021 $ (160 ) $ (9,522 ) $ (4,298 ) $ 385 $ (13,595 ) Other comprehensive income before reclassifications (272 ) — 338 — 66 Amounts reclassified from accumulated other comprehensive income 177 212 — — 389 Net current period other comprehensive income (95 ) 212 338 — 455 As of June 30, 2021 $ (255 ) $ (9,310 ) $ (3,960 ) $ 385 $ (13,140 ) Three Months Ended June 30, 2020 (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption Total As of March 31, 2020 $ (167 ) $ (9,085 ) $ (8,942 ) $ 385 $ (17,809 ) Other comprehensive income before reclassifications 881 — 1,899 — 2,780 Amounts reclassified from accumulated other comprehensive income (loss) (508 ) 191 — — (317 ) Net current period other comprehensive income 373 191 1,899 — 2,463 As of June 30, 2020 $ 206 $ (8,894 ) $ (7,043 ) $ 385 $ (15,346 ) Six Months Ended June 30, 2021 (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption Total As of December 31, 2020 $ 32 $ (9,621 ) $ (2,435 ) $ 385 $ (11,639 ) Other comprehensive income (loss) before reclassifications (329 ) — (1,525 ) — (1,854 ) Amounts reclassified from accumulated other comprehensive income 42 311 — — 353 Net current period other comprehensive income (loss) (287 ) 311 (1,525 ) — (1,501 ) As of June 30, 2021 $ (255 ) $ (9,310 ) $ (3,960 ) $ 385 $ (13,140 ) Six Months Ended June 30, 2020 (In thousands) Unrealized Gains (Losses) on Available- for-Sale Securities Defined Benefit Plan Adjustments Foreign Currency Adjustments ASU 2018-02 Adoption Total As of December 31, 2019 $ (284 ) $ (9,226 ) $ (7,292 ) $ 385 $ (16,417 ) Other comprehensive income (loss) before reclassifications (50 ) — 249 — 199 Amounts reclassified from accumulated other comprehensive income (loss) 540 332 — — 872 Amounts reclassified to retained earnings — — — — — Net current period other comprehensive income (loss) 490 332 249 — 1,071 As of June 30, 2020 $ 206 $ (8,894 ) $ (7,043 ) $ 385 $ (15,346 )
Reclassifications Out of Accumulated Other Comprehensive Income (Loss)	The following tables present the details of reclassifications out of accumulated other comprehensive income (loss): Three Months Ended June 30, 2021 (In thousands) Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Statement Where Net Income Is Presented Unrealized gain (loss) on available-for-sale securities: Net realized loss on sales of securities $ (233 ) Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (307 ) (1) Total reclassifications for the period, before tax (540 ) Tax benefit 151 Total reclassifications for the period, net of tax $ (389 ) (1) A part of the computation of net periodic pension cost, which is included in other income (expense), net in the Condensed Consolidated Statements of Income (Loss). Three Months Ended June 30, 2020 (In thousands) Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Statement Where Net Income Is Presented Unrealized gain (loss) on available-for-sale securities: Net realized gain on sales of securities $ 686 Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (277 ) (1) Total reclassifications for the period, before tax 409 Tax expense (92 ) Total reclassifications for the period, net of tax $ 317 (1) A part of the computation of net periodic pension cost, which is included in other income (expense), net in the Condensed Consolidated Statements of Income (Loss). Six Months Ended June 30, 2021 (In thousands) Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Statement Where Net Income Is Presented Unrealized gain (loss) on available-for-sale securities: Net realized loss on sales of securities $ (55 ) Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (451 ) (1) Total reclassifications for the period, before tax (506 ) Tax benefit 153 Total reclassifications for the period, net of tax $ (353 ) (1) A part of the computation of net periodic pension cost, which is included in other income (expense), net in the Condensed Consolidated Statements of Income (Loss). Six Months Ended June 30, 2020 (In thousands) Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Statement Where Net Income Is Presented Unrealized gain (loss) on available-for-sale securities: Net realized loss on sales of securities $ (730 ) Net investment gain (loss) Defined benefit plan adjustments – actuarial losses (481 ) (1) Total reclassifications for the period, before tax (1,211 ) Tax benefit 339 Total reclassifications for the period, net of tax $ (872 ) (1) A part of the computation of net periodic pension cost, which is included in other income (expense), net in the Condensed Consolidated Statements of Income (Loss).
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): Three Months Ended Three Months Ended June 30, 2021 June 30, 2020 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gain (loss) on available-for-sale securities $ (358 ) $ 86 $ (272 ) $ 1,191 $ (310 ) $ 881 Reclassification adjustment for amounts related to available-for-sale investments included in net income (loss) 233 (56 ) 177 (686 ) 178 (508 ) Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income (loss) 307 (95 ) 212 277 (86 ) 191 Foreign currency translation adjustment 338 — 338 1,899 — 1,899 Total Other Comprehensive Income $ 520 $ (65 ) $ 455 $ 2,681 $ (218 ) $ 2,463 Six Months Ended Six Months Ended June 30, 2021 June 30, 2020 (In thousands) Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Before-Tax Amount Tax (Expense) Benefit Net-of-Tax Amount Unrealized gain (loss) on available-for-sale securities $ (433 ) $ 104 $ (329 ) $ (68 ) $ 18 $ (50 ) Reclassification adjustment for amounts related to available-for-sale investments included in net income 55 (13 ) 42 730 (190 ) 540 Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income 451 (140 ) 311 481 (149 ) 332 Foreign currency translation adjustment (1,525 ) — (1,525 ) 249 — 249 Total Other Comprehensive Income (Loss) $ (1,452 ) $ (49 ) $ (1,501 ) $ 1,392 $ (321 ) $ 1,071

Earnings (Loss) Per Share (Tabl

Earnings (Loss) Per Share (Tables)	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Summary of Calculation of Basic and Diluted Earnings (Loss) Per Share	The calculation of basic and diluted earnings (loss) per share is as follows: Three Months Ended Six Months Ended June 30, June 30, (In thousands, except per share amounts) 2021 2020 2021 2020 Numerator Net income (loss) $ 5,086 $ 752 $ 5,982 $ (9,217 ) Denominator Weighted average number of shares – basic 48,449 47,958 48,393 47,957 Effect of dilutive securities PSUs, RSUs and restricted stock 816 296 722 — Stock options 161 — 110 — Weighted average number of shares – diluted 49,426 48,254 49,225 47,957 Earnings (loss) per share – basic $ 0.10 $ 0.02 $ 0.12 $ (0.19 ) Earnings (loss) per share – diluted $ 0.10 $ 0.02 $ 0.12 $ (0.19 )

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Revenue and Gross Profit of Reportable Segments	The following tables present information about the revenue and gross profit of our reportable segments: Three Months Ended June 30, 2021 June 30, 2020 (In thousands) Revenue Gross Profit Revenue Gross Profit Network Solutions $ 125,449 $ 55,435 $ 111,323 $ 47,252 Services & Support 17,783 7,233 17,392 6,220 Total $ 143,232 $ 62,668 $ 128,715 $ 53,472 Six Months Ended June 30, 2021 June 30, 2020 (In thousands) Revenue Gross Profit Revenue Gross Profit Network Solutions $ 239,258 $ 104,243 $ 208,695 $ 92,998 Services & Support 31,507 12,026 34,543 12,074 Total $ 270,765 $ 116,269 $ 243,238 $ 105,072
Disaggregate of Revenue by Reportable Segment and Revenue Category	The following tables disaggregate revenue by reportable segment and revenue category: Three Months Ended June 30, 2021 June 30, 2020 (In thousands) Network Solutions Services & Support Total Network Solutions Services & Support Total Access & Aggregation $ 78,307 $ 12,657 $ 90,964 $ 69,721 $ 13,055 $ 82,776 Subscriber Solutions & Experience 45,097 2,713 47,810 38,081 2,312 40,393 Traditional & Other Products 2,045 2,413 4,458 3,521 2,025 5,546 Total $ 125,449 $ 17,783 $ 143,232 $ 111,323 $ 17,392 $ 128,715 Six Months Ended June 30, 2021 June 30, 2020 (In thousands) Network Solutions Services & Support Total Network Solutions Services & Support Total Access & Aggregation $ 138,360 $ 21,678 $ 160,038 $ 122,776 $ 25,966 $ 148,742 Subscriber Solutions & Experience 97,366 5,013 102,379 78,064 4,508 82,572 Traditional & Other Products 3,532 4,816 8,348 7,855 4,069 11,924 Total $ 239,258 $ 31,507 $ 270,765 $ 208,695 $ 34,543 $ 243,238 The table below presents revenue information by category: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Access & Aggregation $ 90,964 $ 82,776 $ 160,038 $ 148,742 Subscriber Solutions & Experience 47,810 40,393 102,379 82,572 Traditional & Other Products 4,458 5,546 8,348 11,924 Total $ 143,232 $ 128,715 $ 270,765 $ 243,238
Revenue Information by Geographic Area	The following table presents revenue information by geographic area: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 United States $ 94,656 $ 84,458 $ 181,141 $ 163,449 International 48,576 44,257 89,624 79,789 Total $ 143,232 $ 128,715 $ 270,765 $ 243,238

Liability for Warranty Returns

Liability for Warranty Returns (Tables)	6 Months Ended
	Jun. 30, 2021
Product Warranties Disclosures [Abstract]
Summary of Reversal of Prior Provisions Related to Warranty Expirations	During the three and six months ended June 30, 2021 and 2020, we had a reversal of prior provisions related to warranty expirations, the impact of which is reflected in the table below: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Balance at beginning of period $ 6,472 $ 7,635 $ 7,146 $ 8,394 Plus: Amounts charged to cost and expenses 11 393 (220 ) 338 Less: Deductions (486 ) (734 ) (929 ) (1,438 ) Balance at end of period $ 5,997 $ 7,294 $ 5,997 $ 7,294

Restructuring (Tables)

Restructuring (Tables)	6 Months Ended
	Jun. 30, 2021
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 Condensed Consolidated Balance Sheets is as follows: Three Months Ended Six Months Ended (In thousands) June 30, 2021 June 30, 2021 Balance at beginning of period $ 2,077 $ 4,186 Plus: Amounts charged to cost and expense 8 309 Less: Amounts paid (565 ) (2,975 ) Balance as of June 30, 2021 $ 1,520 $ 1,520 (In thousands) For the Year Ended December 31, 2020 Balance as of December 31, 2019 $ 1,568 Plus: Amounts charged to cost and expense 6,229 Less: Amounts paid (3,611 ) Balance as of December 31, 2020 $ 4,186
Schedule of Components of Restructuring Expenses	Restructuring expenses included in the Condensed Consolidated Statements of Income (Loss) were as follows: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 Cost of revenue $ - $ 22 $ 15 $ 56 Selling, general and administrative expenses 3 489 145 572 Research and development expenses 5 681 149 1,117 Total restructuring expenses $ 8 $ 1,192 $ 309 $ 1,745 Components of restructuring expense by geographic area were as follows: Three Months Ended Six Months Ended June 30, June 30, (In thousands) 2021 2020 2021 2020 United States $ 3 $ 1,192 $ 212 $ 1,743 International 5 — 97 2 Total restructuring expenses $ 8 $ 1,192 $ 309 $ 1,745

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Summary Of Significant Accounting Policy [Line Items]
Tax benefit in other comprehensive income (loss)	$ 65	$ 218		$ 49	$ 321
ASU 2016-13 [Member]
Summary Of Significant Accounting Policy [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true			true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Jan. 1, 2020			Jan. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true			true
ASU 2019-12 [Member]
Summary Of Significant Accounting Policy [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]	true			true
Change in Accounting Principle, Accounting Standards Update, Adoption Date	Apr. 1, 2020			Apr. 1, 2020
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]	true			true
Adjustments for New Accounting Principle, Early Adoption [Member]
Summary Of Significant Accounting Policy [Line Items]
Tax benefit in other comprehensive income (loss)			$ (100)
Overstatement Long-term Investment Balance at Remeasured Cost Basis [Member]
Summary Of Significant Accounting Policy [Line Items]
Amount of revision			2,800
Errors in Net Investment Gain [Member]
Summary Of Significant Accounting Policy [Line Items]
Amount of revision			$ 1,500

Cash, Cash Equivalents and Re_3

Cash, Cash Equivalents and Restricted Cash - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 69,927	$ 60,161
Restricted cash	54	18
Cash, cash equivalents and restricted cash	$ 69,981	$ 60,179

Revenue - Additional Informatio

Revenue - Additional Information (Detail)	3 Months Ended	6 Months Ended
	Jun. 30, 2021USD ($)	Jun. 30, 2021USD ($)Category	Dec. 31, 2020USD ($)
Revenue [Line Items]
Number of categories | Category		3
Remaining performance obligations	$ 0	$ 0
Recognized revenue	2,900,000	7,900,000
Other Than Maintenance Services [Member]
Revenue [Line Items]
Remaining performance obligations	$ 19,700,000	$ 19,700,000	$ 17,700,000

Revenue - Disaggregate of Reven

Revenue - Disaggregate of Revenue by Reportable Segment and Revenue Category (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation Of Revenue [Line Items]
Revenue	$ 143,232	$ 128,715	$ 270,765	$ 243,238
Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue	90,964	82,776	160,038	148,742
Subscriber Solutions & Experience [Member]
Disaggregation Of Revenue [Line Items]
Revenue	47,810	40,393	102,379	82,572
Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue	4,458	5,546	8,348	11,924
Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue	125,449	111,323	239,258	208,695
Network Solutions [Member] | Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue	78,307	69,721	138,360	122,776
Network Solutions [Member] | Subscriber Solutions & Experience [Member]
Disaggregation Of Revenue [Line Items]
Revenue	45,097	38,081	97,366	78,064
Network Solutions [Member] | Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue	2,045	3,521	3,532	7,855
Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue	17,783	17,392	31,507	34,543
Services & Support [Member] | Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue	12,657	13,055	21,678	25,966
Services & Support [Member] | Subscriber Solutions & Experience [Member]
Disaggregation Of Revenue [Line Items]
Revenue	2,713	2,312	5,013	4,508
Services & Support [Member] | Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue	$ 2,413	$ 2,025	$ 4,816	$ 4,069

Revenue - Additional Informat_2

Revenue - Additional Information (Detail1) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-07-01	Jun. 30, 2021
Revenue [Line Items]
Remaining performance obligations, percentage	64.00%
Remaining performance obligations, period	12 months

Revenue - Information about Rec

Revenue - Information about Receivables, Contract Assets, and Unearned Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Revenue From Contract With Customer [Abstract]
Accounts receivable, net	$ 122,669	$ 98,827
Contract assets	1,036	63
Unearned revenue	15,889	14,092
Non-current unearned revenue	$ 7,030	$ 6,888

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Income Tax Disclosure [Line Items]
Effective tax rate expense (benefit)	18.10%	68.50%	26.70%	22.90%
Income tax benefit, result of CARES act of 2020				$ 7,400
Income tax expense, result of Alabama business tax competitiveness act			$ 1,600
Deferred tax assets, gross	$ 56,941		56,941		$ 55,687
Valuation allowance established against deferred tax assets	47,776		47,776		45,818
Deferred tax assets	9,165		9,165		9,869
Domestic [Member]
Income Tax Disclosure [Line Items]
Valuation allowance established against deferred tax assets			1,600
Deferred tax assets, gross	45,383		45,383		43,791
Valuation allowance established against deferred tax assets	$ 45,383		$ 45,383		$ 43,791

Income Taxes - Summary of Suppl

Income Taxes - Summary of Supplemental Balance Sheet Information Related to Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets	$ 56,941	$ 55,687
Valuation Allowance	(47,776)	(45,818)
Deferred Tax Assets, net	9,165	9,869
Domestic [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets	45,383	43,791
Valuation Allowance	(45,383)	(43,791)
International [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets	11,558	11,896
Valuation Allowance	(2,393)	(2,027)
Deferred Tax Assets, net	$ 9,165	$ 9,869

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense Related to Stock Options, PSUs, RSUs and Restricted Stock (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,808	$ 1,655	$ 3,615	$ 3,446
Tax benefit for expense associated with stock options, PSUs, RSUs and restricted stock	(452)	(394)	(883)	(821)
Total stock-based compensation expense, net of tax	1,356	1,261	2,732	2,625
Stock-based Compensation Expense Included in Cost of Revenue [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	125	87	256	202
Selling, General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,098	971	2,196	2,046
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	585	597	1,163	1,198
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	$ 1,683	$ 1,568	$ 3,359	$ 3,244

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of PSUs, RSUs and Restricted Stock Outstanding (Detail) shares in Thousands	6 Months Ended
	Jun. 30, 2021$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Unvested PSUs, RSUs and restricted stock outstanding, beginning balance | shares	1,846
Number of Shares, PSUs, RSUs and restricted stock granted | shares	357
Number of Shares, PSUs, RSUs and restricted stock vested | shares	(12)
Number of Shares, PSUs, RSUs and restricted stock forfeited | shares	(47)
Number of Shares, Unvested PSUs, RSUs and restricted stock outstanding, ending balance | shares	2,144
Weighted Avg. Grant Date Fair Value, Unvested PSUs, RSUs and restricted stock outstanding, Beginning Balance | $ / shares	$ 11.49
Weighted Avg. Grant Date Fair Value, PSUs, RSUs and restricted stock granted | $ / shares	16.73
Weighted Avg. Grant Date Fair Value, PSUs, RSUs and restricted stock vested | $ / shares	11.76
Weighted Avg. Grant Date Fair Value, PSUs, RSUs and restricted stock forfeited | $ / shares	11.58
Weighted Avg. Grant Date Fair Value, Unvested PSUs, RSUs and restricted stock outstanding, Ending Balance | $ / shares	$ 12.41

Stock-Based Compensation (PSUs,

Stock-Based Compensation (PSUs, RSUs and Restricted Stock) - Additional Information (Detail) - USD ($) shares in Thousands, $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share granted	357
Options available for issuance under stockholders-approved equity plan	3,500
Performance Stock Units (PSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share granted	300	300
Vesting period	2 years	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%	142.80%
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	$ 13.2
Recognition period of unvested compensation expense	2 years 6 months
Performance-Based PSUs [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation expense related to other than options	$ 7.5
Recognition period of unvested compensation expense	1 year 6 months

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Options Outstanding (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Stock Options, Stock options outstanding, Beginning Balance	2,718
Number of Stock Options, Stock options exercised	(215)
Number of Stock Options, Stock options expired	(117)
Number of Stock Options, Stock options outstanding, Ending Balance	2,386	2,718
Number of Stock Options, Stock options exercisable	2,386
Weighted Avg. Exercise Price, Stock options outstanding, Beginning Balance	$ 21.17
Weighted Avg. Exercise Price, Stock options exercised	16.53
Weighted Avg. Exercise Price, Stock options expired	23.37
Weighted Avg. Exercise Price, Stock options outstanding, Ending Balance	21.47	$ 21.17
Weighted Avg. Exercise Price, Stock options exercisable	$ 21.47
Weighted Avg. Remaining Contractual Life In Years, Stock options outstanding	2 years 4 months 24 days	2 years 10 months 24 days
Weighted Avg. Remaining Contractual Life in Years, Stock options exercisable	2 years 4 months 24 days
Aggregate Intrinsic Value, Stock options exercised	$ 588
Aggregate Intrinsic Value, Stock options expired	17
Aggregate Intrinsic Value, Stock options outstanding	4,721
Aggregate Intrinsic Value, Stock options exercisable	$ 4,721

Stock-Based Compensation (Stock

Stock-Based Compensation (Stock Options) - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Unrecognized compensation expense related to stock options	$ 0
Number of Stock options, granted	0	0
Aggregate intrinsic value based on fair market value	$ 4,721,000
Total pre-tax intrinsic value of options exercised	$ 588,000

Investments - Debt Securities a

Investments - Debt Securities and Other Investments, Included on Condensed Consolidated Balance Sheet and Recorded at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 44,320	$ 44,666
Gross Unrealized Gains	190	457
Gross Unrealized Losses	(30)	(7)
Fair Value	44,480	45,116
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,954	11,762
Gross Unrealized Gains	53	123
Gross Unrealized Losses	(6)
Fair Value	15,001	11,885
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,523	2,854
Gross Unrealized Gains	15	30
Gross Unrealized Losses	(1)
Fair Value	2,537	2,884
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,983	6,634
Gross Unrealized Gains	20	74
Gross Unrealized Losses	(2)
Fair Value	4,001	6,708
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,004	11,536
Gross Unrealized Gains	50	114
Gross Unrealized Losses	(15)	(6)
Fair Value	11,039	11,644
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,777	9,763
Gross Unrealized Gains	51	112
Gross Unrealized Losses	(5)
Fair Value	10,823	9,875
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	546	1,334
Gross Unrealized Gains	1	4
Gross Unrealized Losses	(1)	(1)
Fair Value	546	1,337
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		250
Fair Value		250
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	533	533
Fair Value	$ 533	$ 533

Investments - Contractual Matur

Investments - Contractual Maturities of Debt Securities and Other Investments (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Fair Value/Carrying Value	$ 44,480	$ 45,116
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	436
One to two years	4,575
Two to three years	7,518
Three to five years	2,472
Available-for-sale debt securities, Fair Value/Carrying Value	15,001	11,885
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	529
One to two years	496
Two to three years	1,103
Three to five years	409
Available-for-sale debt securities, Fair Value/Carrying Value	2,537	2,884
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	1
Two to three years	50
Three to five years	1,749
Five to ten years	866
More than ten years	1,335
Available-for-sale debt securities, Fair Value/Carrying Value	4,001	6,708
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	254
One to two years	1,865
Two to three years	1,199
Three to five years	165
Five to ten years	2,213
More than ten years	5,343
Available-for-sale debt securities, Fair Value/Carrying Value	11,039	11,644
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than one year	735
One to two years	7,240
Two to three years	1,188
Three to five years	1,660
Available-for-sale debt securities, Fair Value/Carrying Value	10,823	9,875
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Two to three years	546
Available-for-sale debt securities, Fair Value/Carrying Value	546	1,337
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	$ 533

Investments - Gross Realized Ga

Investments - Gross Realized Gains and Losses on Sale of Debt Securities (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Gross realized gain on debt securities	$ 97	$ 190	$ 184	$ 233
Gross realized loss on debt securities	(20)	(19)	(36)	(39)
Total gain recognized, net	$ 77	$ 171	$ 148	$ 194

Investments - Additional Inform

Investments - Additional Information (Detail) - USD ($)	3 Months Ended	6 Months Ended		12 Months Ended
	Mar. 31, 2019	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Schedule of Investments [Line Items]
Available-for-sale debt securities, allowance for credit loss		$ 0	$ 0
Purchase an available-for-sale debt securities with credit deterioration		0
Transfer from investments	$ 3,400,000
Asset impairments			$ 65,000
Carrying value of investment		800,000		$ 800,000
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 - Realized and Unre

Investments - Realized and Unrealized Gains and Losses related to Marketable Equity Securities (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]
Realized gain (loss) on equity securities sold	$ (79)	$ 328	$ (55)	$ (2,108)
Unrealized gain on equity securities held	2,011	9,353	2,912	889
Total gain (loss) recognized, net	$ 1,932	$ 9,681	$ 2,857	$ (1,219)

Investments - Cash Equivalents

Investments - Cash Equivalents and Investments held at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	$ 44,480	$ 45,116
Marketable equity securities	800	800
Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Other investments	1,400	1,400
Total	85,719	82,217
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	1,400
Total	50,812	46,976
Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule of Available-for-sale Securities [Line Items]
Total	34,374	34,708
Fair Value, Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member]
Schedule of Available-for-sale Securities [Line Items]
Total	533	533
Money Market Funds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents	615	497
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	615	497
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]
Cash equivalents	1,250
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]
Cash equivalents	1,250
Available-for-sale debt securities		250
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	15,001	11,885
Corporate Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	15,001	11,885
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	15,001	11,885
Municipal Fixed-Rate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	2,537	2,884
Municipal Fixed-Rate Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	2,537	2,884
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	2,537	2,884
Asset-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	4,001	6,708
Asset-Backed Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	4,001	6,708
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	4,001	6,708
Mortgage/Agency-Backed Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	11,039	11,644
Mortgage/Agency-Backed Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	11,039	11,644
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	11,039	11,644
U.S. Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	10,823	9,875
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	10,823	9,875
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	10,823	9,875
Foreign Government Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	546	1,337
Foreign Government Bonds [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	546	1,337
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	546	1,337
Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	533	533
Other [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities	533	533
Other [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	533
Marketable Equity Securities - Various Industries [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable equity securities	12,057	10,963
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	12,057	10,963
Deferred Compensation Plan Assets [Member] | Fair Value, Measurements [Member]
Schedule of Available-for-sale Securities [Line Items]
Marketable equity securities	25,917	23,891
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	$ 25,917	$ 23,891

Inventory - Components of Inven

Inventory - Components of Inventory (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Raw materials	$ 52,257	$ 47,026
Work in process	1,874	776
Finished goods	64,881	77,655
Total inventory, net	$ 119,012	$ 125,457

Inventory - Additional Informat

Inventory - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Inventory valuation reserves	$ 42.7	$ 39.6

Property, Plant and Equipment -

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Land	$ 4,575	$ 4,575
Building and land improvements	34,961	35,142
Building	68,161	68,169
Furniture and fixtures	19,936	19,965
Computer hardware and software	71,262	70,942
Engineering and other equipment	134,090	132,920
Total property, plant and equipment	332,985	331,713
Less: accumulated depreciation	(274,715)	(269,314)
Total property, plant and equipment, net	$ 58,270	$ 62,399

Property, Plant and Equipment_2

Property, Plant and Equipment - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Property Plant And Equipment [Abstract]
Impairment losses of long-lived assets	$ 0	$ 0	$ 0	$ 0
Depreciation	$ 3,000,000	$ 3,000,000	$ 6,100,000	$ 6,000,000

Goodwill - Additional Informati

Goodwill - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Goodwill [Line Items]
Goodwill			$ 7,000,000		$ 7,000,000
Impairment of goodwill	$ 0	$ 0	0	$ 0
Network Solutions [Member]
Goodwill [Line Items]
Goodwill			6,600,000		6,600,000
Services & Support [Member]
Goodwill [Line Items]
Goodwill			$ 400,000		$ 400,000

Intangible Assets - Summary of

Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 36,355	$ 39,293
Accumulated Amortization	(15,001)	(15,823)
Net Book Value	21,354	23,470
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	20,985	21,123
Accumulated Amortization	(9,030)	(8,055)
Net Book Value	11,955	13,068
Developed Technology [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	8,200	8,200
Accumulated Amortization	(3,114)	(2,546)
Net Book Value	5,086	5,654
Licensed Technology [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,900	5,900
Accumulated Amortization	(2,158)	(1,830)
Net Book Value	3,742	4,070
Supplier Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount		2,800
Accumulated Amortization		(2,800)
Licensing Agreements [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	560	560
Accumulated Amortization	(189)	(152)
Net Book Value	371	408
Patent [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	500	500
Accumulated Amortization	(329)	(294)
Net Book Value	171	206
Trade Names [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	210	210
Accumulated Amortization	(181)	(146)
Net Book Value	$ 29	$ 64

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Intangible Assets Net Excluding Goodwill [Abstract]
Impairment losses of intangible assets	$ 0	$ 0	$ 0	$ 0
Amortization expense	$ 1,000,000	$ 1,000,000	$ 2,100,000	$ 2,400,000

Intangible Assets - Estimated F

Intangible Assets - Estimated Future Amortization Expense Related to Intangible Assets (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
2021	$ 2,028
2022	3,485
2023	3,333
2024	3,238
2025	3,029
Thereafter	6,241
Net Book Value	$ 21,354	$ 23,470

Leases - Net Investment in Sale

Leases - Net Investment in Sales-Type Leases (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Sales Type Leases Net Investment In Leases [Abstract]
Current minimum lease payments receivable	$ 103	$ 702
Non-current minimum lease payments receivable	13	347
Total minimum lease payments receivable	116	1,049
Less: Current unearned revenue	60	218
Less: Non-current unearned revenue	2	50
Net investment in sales-type leases	$ 54	$ 781

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	Jun. 30, 2021
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	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2008	Jan. 13, 1995
Debt Instrument [Line Items]
Repayment of bond			$ 24,600
Taxable Revenue Bonds [Member]
Debt Instrument [Line Items]
Proceeds from state industrial development authority issued taxable bonds loaned to ADTRAN				$ 50,000	$ 20,000
Percentage of interest on bond		2.00%
Maturity date of bond		Jan. 1, 2020
Repayment of bond	$ 24,600

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2021shares
Equity [Abstract]
Stock repurchased, shares	0
Additional shares authorized for purchase	2,500,000
Maximum shares authorized for repurchase, prior and new announcements and total after new announcement	5,000,000

Stockholders' Equity - Changes

Stockholders' Equity - Changes in Accumulated Other Comprehensive Loss, Net of Tax by Component (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 370,375	$ 363,715	$ 372,944	$ 380,426
Other comprehensive income (loss) before reclassifications	66	2,780	(1,854)	199
Amounts reclassified from accumulated other comprehensive income (loss)	389	(317)	353	872
Net current period other comprehensive income (loss)	455	2,463	(1,501)	1,071
Ending Balance	375,515	364,194	375,515	364,194
ASU 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	385	385	385	385
Ending Balance	385	385	385	385
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(13,595)	(17,809)	(11,639)	(16,417)
Ending Balance	(13,140)	(15,346)	(13,140)	(15,346)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(160)	(167)	32	(284)
Other comprehensive income (loss) before reclassifications	(272)	881	(329)	(50)
Amounts reclassified from accumulated other comprehensive income (loss)	177	(508)	42	540
Net current period other comprehensive income (loss)	(95)	373	(287)	490
Ending Balance	(255)	206	(255)	206
Defined Benefit Plan Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(9,522)	(9,085)	(9,621)	(9,226)
Amounts reclassified from accumulated other comprehensive income (loss)	212	191	311	332
Net current period other comprehensive income (loss)	212	191	311	332
Ending Balance	(9,310)	(8,894)	(9,310)	(8,894)
Foreign Currency Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(4,298)	(8,942)	(2,435)	(7,292)
Other comprehensive income (loss) before reclassifications	338	1,899	(1,525)	249
Net current period other comprehensive income (loss)	338	1,899	(1,525)	249
Ending Balance	$ (3,960)	$ (7,043)	$ (3,960)	$ (7,043)

Stockholders' Equity - Reclassi

Stockholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (Loss) Before Income Taxes	$ 6,213		$ 2,387		$ 8,157	$ (11,950)
Tax benefit (expense)	(1,127)		(1,635)		(2,175)	2,733
Net Income (Loss)	5,086	$ 896	752	$ (9,969)	5,982	(9,217)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Income (Loss) Before Income Taxes	(540)		409		(506)	(1,211)
Tax benefit (expense)	151		(92)		153	339
Net Income (Loss)	(389)		317		(353)	(872)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Net investment gain (loss)	(233)		686		(55)	(730)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Other Income (Expense), Net [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined benefit plan adjustments – actuarial losses	$ (307)		$ (277)		$ (451)	$ (481)

Stockholders' Equity - Tax Effe

Stockholders' Equity - Tax Effects Related to the Change in Each Component of Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Equity [Abstract]
Unrealized gain (loss) on available-for-sale securities, Before-Tax Amount	$ (358)		$ 1,191		$ (433)	$ (68)
Unrealized gain (loss) on available-for-sale securities, Tax (Expense) Benefit	86		(310)		104	18
Unrealized gain (loss) on available-for-sale securities, Net-of-Tax Amount	(272)		881		(329)	(50)
Reclassification adjustment for amounts related to available-for-sale investments included in net income (loss), Before-Tax Amount	233		(686)		55	730
Reclassification adjustment for amounts related to available-for-sale investments included in net income (loss), Tax (Expense) Benefit	(56)		178		(13)	(190)
Reclassification adjustment for amounts related to available-for-sale investments included in net income (loss), Net-of-Tax Amount	177		(508)		42	540
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income (loss), Before-Tax Amount	307		277		451	481
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income (loss), Tax (Expense) Benefit	(95)		(86)		(140)	(149)
Reclassification adjustment for amounts related to defined benefit plan adjustments included in net income (loss), Net-of-Tax Amount	212		191		311	332
Foreign currency translation adjustment, Before-Tax Amount	338		1,899		(1,525)	249
Foreign currency translation adjustment, Net-of-Tax Amount	338		1,899		(1,525)	249
Total Other Comprehensive Income (Loss), Before-Tax Amount	520		2,681		(1,452)	1,392
Total Other Comprehensive Income (Loss), Tax (Expense) Benefit	(65)		(218)		(49)	(321)
Other Comprehensive Income (Loss), net of tax	$ 455	$ (1,956)	$ 2,463	$ (1,392)	$ (1,501)	$ 1,071

Earnings (Loss) Per Share - Sum

Earnings (Loss) Per Share - Summary of Calculation of Basic and Diluted Earnings (Loss) Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator
Net income (loss)	$ 5,086	$ 896	$ 752	$ (9,969)	$ 5,982	$ (9,217)
Denominator
Weighted average number of shares – basic	48,449		47,958		48,393	47,957
Effect of dilutive securities
PSUs, RSUs and restricted stock	816		296		722
Stock options	161				110
Weighted average number of shares – diluted	49,426		48,254		49,225	47,957
Earnings (loss) per share – basic	$ 0.10		$ 0.02		$ 0.12	$ (0.19)
Earnings (loss) per share – diluted	$ 0.10		$ 0.02		$ 0.12	$ (0.19)

Earnings (Loss) Per Share - Add

Earnings (Loss) Per Share - Additional Information (Detail) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive effect excluded calculation of diluted earnings per share	400	1,900	600	2,300
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 per share	1	15	3	100

Segment Information - Additiona

Segment Information - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2021CategorySegment
Segment Reporting [Abstract]
Number of reportable segments | Segment	2
Number of categories | Category	3

Segment Information - Revenue a

Segment Information - Revenue and Gross Profit of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenue	$ 143,232	$ 128,715	$ 270,765	$ 243,238
Gross Profit	62,668	53,472	116,269	105,072
Network Solutions [Member]
Segment Reporting Information [Line Items]
Revenue	125,449	111,323	239,258	208,695
Gross Profit	55,435	47,252	104,243	92,998
Services & Support [Member]
Segment Reporting Information [Line Items]
Revenue	17,783	17,392	31,507	34,543
Gross Profit	$ 7,233	$ 6,220	$ 12,026	$ 12,074

Segment Information - Revenue I

Segment Information - Revenue Information by Category (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation Of Revenue [Line Items]
Revenue	$ 143,232	$ 128,715	$ 270,765	$ 243,238
Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue	90,964	82,776	160,038	148,742
Subscriber Solutions & Experience [Member]
Disaggregation Of Revenue [Line Items]
Revenue	47,810	40,393	102,379	82,572
Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue	$ 4,458	$ 5,546	$ 8,348	$ 11,924

Segment Information - Revenue_2

Segment Information - Revenue Information by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue from External Customer [Line Items]
Revenue	$ 143,232	$ 128,715	$ 270,765	$ 243,238
United States [Member]
Revenue from External Customer [Line Items]
Revenue	94,656	84,458	181,141	163,449
International [Member]
Revenue from External Customer [Line Items]
Revenue	$ 48,576	$ 44,257	$ 89,624	$ 79,789

Liability for Warranty Return_2

Liability for Warranty Returns - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Product Warranties Disclosures [Abstract]
Period of assurance-based warranty for product defects	90 days to five years
Liability for warranty obligations	$ 5,997	$ 6,472	$ 7,146	$ 7,294	$ 7,635	$ 8,394

Liability for Warranty Return_3

Liability for Warranty Returns - Summary of Reversal of Prior Provisions Related to Warranty Expirations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Product Warranties Disclosures [Abstract]
Balance at beginning of period	$ 6,472	$ 7,635	$ 7,146	$ 8,394
Plus: Amounts charged to cost and expenses	11	393	(220)	338
Less: Deductions	(486)	(734)	(929)	(1,438)
Balance at end of period	$ 5,997	$ 7,294	$ 5,997	$ 7,294

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Mar. 31, 2020Officer	Jun. 30, 2021USD ($)	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Contingencies And Commitments [Line Items]
Commitments related to performance bonds		$ 21,200,000		$ 15,200,000
Commitments related to performance bonds expiration month and year		2024-08
Letter of credit secured by pledge of a portion of fixed income securities		$ 18,200,000
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		18,200,000
Minimum [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
Former Executive Officers [Member]
Contingencies And Commitments [Line Items]
Number of officers | Officer	1

Restructuring - Additional Info

Restructuring - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Restructuring And Related Activities [Abstract]
Cumulative amount of restructuring expenses incurred for restructuring plan	$ 12.5

Restructuring - Schedule of Rec

Restructuring - Schedule of Reconciliation of Restructuring Liability (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Balance at beginning of period	$ 2,077		$ 4,186	$ 1,568	$ 1,568
Plus: Amounts charged to cost and expense	8	$ 1,192	309	$ 1,745	6,229
Less: Amounts paid	(565)		(2,975)		(3,611)
Balance at end of period	$ 1,520		$ 1,520		$ 4,186

Restructuring - Schedule of Com

Restructuring - Schedule of Components of Restructuring Expenses Including in Condensed Consolidated Statements of Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	$ 8	$ 1,192	$ 309	$ 1,745	$ 6,229
Cost of Revenue [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses		22	15	56
Selling, General and Administrative Expenses [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	3	489	145	572
Research and Development Expenses [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	$ 5	$ 681	$ 149	$ 1,117

Restructuring - Schedule of C_2

Restructuring - Schedule of Components of Restructuring Expense by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	$ 8	$ 1,192	$ 309	$ 1,745	$ 6,229
United States [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	3	$ 1,192	212	1,743
International [Member]
Restructuring Cost And Reserve [Line Items]
Total restructuring expenses	$ 5		$ 97	$ 2

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Aug. 04, 2021	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Sep. 02, 2021
Subsequent Event [Line Items]
Common stock dividends per share declared		$ 0.09	$ 0.09	$ 0.09	$ 0.09
Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend declaration date	Aug. 4, 2021
Common stock dividends per share declared	$ 0.09
Dividend record date	Aug. 19, 2021
Dividend payment date	Sep. 2, 2021
Scenario Forecast [Member]
Subsequent Event [Line Items]
Quarterly dividend payable, aggregate amount						$ 4.4