Unaudited Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Additional Paid-in Capital 2023 Notes	Additional Paid-in Capital 2025 Notes	Accumulated Other Comprehensive Loss	Treasury Stock	Retained Earnings	Retained Earnings Cumulative effect, period of adoption, adjustment
Balance at Dec. 31, 2018		$ 48	$ 437,250			$ (2,588)	$ (233,676)	$ 152,650
Balance (in shares) at Dec. 31, 2018		31,771,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation related to restricted stock vesting and retirement savings plan contributions		$ 1	12,451
Proceeds from the sales of stock through the Employee Stock Purchase Plan (in shares)		5,000
Proceeds from the sales of stock through the Employee Stock Purchase Plan			130
Stock compensation related to restricted stock vesting and retirement savings plan contributions (in shares)		439,000
Issuance of stock in conjunction with acquisition including stock attributed to future compensation			1,456
Equity component of convertible notes				$ 0	$ 0
Proceeds from sale of hedges related to 2023 convertible notes				0
Purchases of warrants related to 2023 convertible notes				0
Debt issuance costs of 2025 convertible notes allocated to equity, net of tax			0
Purchase of hedges on 2025 convertible notes, net of tax			0
Proceeds from issuance of warrants on 2025 convertible notes
Purchases of treasury stock and buyback of shares for taxes (in shares)		(819,000)
Foreign currency translation adjustment	$ (48)					(48)
Purchases of treasury stock and buyback of shares for taxes							(23,759)
Issuance of stock in conjunction with acquisition (in shares)		54,000
Net income	25,333							25,333
Balance at Sep. 30, 2019	$ 369,248	$ 49	451,287			(2,636)	(257,435)	177,983
Balance (in shares) at Sep. 30, 2019	31,450,000	31,450,000
Balance at Jun. 30, 2019		$ 49	447,146			(2,351)	(253,901)	168,204
Balance (in shares) at Jun. 30, 2019	31,526,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation related to restricted stock vesting and retirement savings plan contributions		0	4,096
Proceeds from the sales of stock through the Employee Stock Purchase Plan (in shares)	1,000
Proceeds from the sales of stock through the Employee Stock Purchase Plan			45
Stock compensation related to restricted stock vesting and retirement savings plan contributions (in shares)	25,000
Issuance of stock in conjunction with acquisition including stock attributed to future compensation			0
Equity component of convertible notes				0	0
Proceeds from sale of hedges related to 2023 convertible notes				0
Purchases of warrants related to 2023 convertible notes				0
Debt issuance costs of 2025 convertible notes allocated to equity, net of tax			0
Purchase of hedges on 2025 convertible notes, net of tax			0
Proceeds from issuance of warrants on 2025 convertible notes			0
Purchases of treasury stock and buyback of shares for taxes (in shares)	(102,000)
Foreign currency translation adjustment	$ (285)					(285)
Purchases of treasury stock and buyback of shares for taxes							(3,534)
Issuance of stock in conjunction with acquisition (in shares)	0
Net income	$ 9,779							9,779
Balance at Sep. 30, 2019	$ 369,248	$ 49	451,287			(2,636)	(257,435)	177,983
Balance (in shares) at Sep. 30, 2019	31,450,000	31,450,000
Balance at Dec. 31, 2019	$ 381,015	$ 49	455,465			(2,650)	(261,624)	189,775	$ (315)
Balance (in shares) at Dec. 31, 2019	31,686,991	31,687,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation related to restricted stock vesting and retirement savings plan contributions		$ 1	13,824
Proceeds from the sales of stock through the Employee Stock Purchase Plan (in shares)		7,000
Proceeds from the sales of stock through the Employee Stock Purchase Plan			210
Stock compensation related to restricted stock vesting and retirement savings plan contributions (in shares)		380,000
Issuance of stock in conjunction with acquisition including stock attributed to future compensation			10,184
Equity component of convertible notes				(49,856)	36,386
Proceeds from sale of hedges related to 2023 convertible notes				47,338
Purchases of warrants related to 2023 convertible notes				(40,699)
Debt issuance costs of 2025 convertible notes allocated to equity, net of tax			(1,155)
Purchase of hedges on 2025 convertible notes, net of tax			(36,387)
Proceeds from issuance of warrants on 2025 convertible notes			22,218
Purchases of treasury stock and buyback of shares for taxes (in shares)		(369,000)
Foreign currency translation adjustment	$ (2,126)					(2,126)
Purchases of treasury stock and buyback of shares for taxes							(15,973)
Issuance of stock in conjunction with acquisition (in shares)		337,000
Net income	21,760							21,760
Balance at Sep. 30, 2020	$ 386,425	$ 50	457,528			(4,776)	(277,597)	211,220	0
Balance (in shares) at Sep. 30, 2020	32,041,550	32,042,000
Balance at Jun. 30, 2020		$ 50	475,147			(3,702)	(266,485)	205,043
Balance (in shares) at Jun. 30, 2020	32,272,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock compensation related to restricted stock vesting and retirement savings plan contributions		0	4,419
Proceeds from the sales of stock through the Employee Stock Purchase Plan (in shares)	3,000
Proceeds from the sales of stock through the Employee Stock Purchase Plan			94
Stock compensation related to restricted stock vesting and retirement savings plan contributions (in shares)	22,000
Issuance of stock in conjunction with acquisition including stock attributed to future compensation			23
Equity component of convertible notes				(49,856)	$ 36,386
Proceeds from sale of hedges related to 2023 convertible notes				47,338
Purchases of warrants related to 2023 convertible notes				$ (40,699)
Debt issuance costs of 2025 convertible notes allocated to equity, net of tax			(1,155)
Purchase of hedges on 2025 convertible notes, net of tax			(36,387)
Proceeds from issuance of warrants on 2025 convertible notes			22,218
Purchases of treasury stock and buyback of shares for taxes (in shares)	(255,000)
Foreign currency translation adjustment	$ (1,074)					(1,074)
Purchases of treasury stock and buyback of shares for taxes							(11,112)
Issuance of stock in conjunction with acquisition (in shares)	0
Net income	$ 6,177							6,177
Balance at Sep. 30, 2020	$ 386,425	$ 50	$ 457,528			$ (4,776)	$ (277,597)	$ 211,220	$ 0
Balance (in shares) at Sep. 30, 2020	32,041,550	32,042,000