Unaudited Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss	Treasury Stock	Retained Earnings
Balance at Dec. 31, 2017		$ 47	$ 403,906	$ (1,822)	$ (163,871)	$ 128,091
Balance (in shares) at Dec. 31, 2017		33,250,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from the sales of stock through the Employee Stock Purchase Plan (in shares)		6,000
Proceeds from the sales of stock through the Employee Stock Purchase Plan			124
Stock compensation related to restricted stock vesting and retirement savings plan contributions (in shares)		421,000
Stock compensation related to restricted stock vesting and retirement savings plan contributions		$ 1	11,559
Equity component of convertible notes, net of tax			15,547
Debt issuance costs of convertible notes, net of tax			(511)
Purchase of hedges on convertible notes, net tax			(15,376)
Proceeds from issuance of warrants on convertible notes			12,060
Purchases of treasury stock and buyback of shares for taxes (in shares)		(1,943,000)
Purchases of treasury stock and buyback of shares for taxes					(54,717)
Surrender of stock in conjunction with net working capital settlement (in shares)		(14,000)
Surrender of stock in conjunction with net working capital settlement					(303)
Issuance of stock in conjunction with acquisition			4,201
Issuance of stock in conjunction with acquisition (in shares)		201,000
Foreign currency translation adjustment	$ (1,015)			(1,015)
Net income	17,083					17,083
Balance at Sep. 30, 2018	$ 355,004	$ 48	431,510	(2,837)	(218,891)	145,174
Balance (in shares) at Sep. 30, 2018		31,921,000
Balance (in shares) at Dec. 31, 2018	0
Balance at Dec. 31, 2017		$ 47	403,906	(1,822)	(163,871)	128,091
Balance (in shares) at Dec. 31, 2017		33,250,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Equity component of convertible notes, net of tax	$ 15,547
Debt issuance costs of convertible notes, net of tax	523
Balance at Dec. 31, 2018	$ 353,684	$ 48	437,250	(2,588)	(233,676)	152,650
Balance (in shares) at Dec. 31, 2018	31,770,888	31,771,000
Balance at Jun. 30, 2018		$ 48	414,610	(2,474)	(177,301)	138,869
Balance (in shares) at Jun. 30, 2018		33,228,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from the sales of stock through the Employee Stock Purchase Plan (in shares)		2,000
Proceeds from the sales of stock through the Employee Stock Purchase Plan			43
Stock compensation related to restricted stock vesting and retirement savings plan contributions (in shares)		29,000
Stock compensation related to restricted stock vesting and retirement savings plan contributions		$ 0	3,945
Equity component of convertible notes, net of tax			15,547
Debt issuance costs of convertible notes, net of tax			(511)
Purchase of hedges on convertible notes, net tax			(15,376)
Proceeds from issuance of warrants on convertible notes			12,060
Purchases of treasury stock and buyback of shares for taxes (in shares)		(1,386,000)
Purchases of treasury stock and buyback of shares for taxes					(41,590)
Surrender of stock in conjunction with net working capital settlement (in shares)		0
Surrender of stock in conjunction with net working capital settlement					0
Issuance of stock in conjunction with acquisition			1,192
Issuance of stock in conjunction with acquisition (in shares)		48,000
Foreign currency translation adjustment	$ (363)			(363)
Net income	6,305					6,305
Balance at Sep. 30, 2018	$ 355,004	$ 48	431,510	(2,837)	(218,891)	145,174
Balance (in shares) at Sep. 30, 2018		31,921,000
Balance (in shares) at Sep. 30, 2019	0
Balance at Dec. 31, 2018	$ 353,684	$ 48	437,250	(2,588)	(233,676)	152,650
Balance (in shares) at Dec. 31, 2018	31,770,888	31,771,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
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
Stock compensation related to restricted stock vesting and retirement savings plan contributions		$ 1	12,451
Equity component of convertible notes, net of tax	$ 15,547		0
Debt issuance costs of convertible notes, net of tax	523		0
Purchase of hedges on convertible notes, net tax			0
Proceeds from issuance of warrants on convertible notes			0
Purchases of treasury stock and buyback of shares for taxes (in shares)		(819,000)
Purchases of treasury stock and buyback of shares for taxes					(23,759)
Surrender of stock in conjunction with net working capital settlement (in shares)		0
Surrender of stock in conjunction with net working capital settlement					0
Issuance of stock in conjunction with acquisition			1,456
Issuance of stock in conjunction with acquisition (in shares)		54,000
Foreign currency translation adjustment	(48)			(48)
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	31,449,931	31,450,000
Balance (in shares) at Sep. 30, 2019	0
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]
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
Stock compensation related to restricted stock vesting and retirement savings plan contributions		$ 0	4,096
Equity component of convertible notes, net of tax			0
Debt issuance costs of convertible notes, net of tax			0
Purchase of hedges on convertible notes, net tax			0
Proceeds from issuance of warrants on convertible notes			0
Purchases of treasury stock and buyback of shares for taxes (in shares)		(102,000)
Purchases of treasury stock and buyback of shares for taxes					(3,534)
Surrender of stock in conjunction with net working capital settlement (in shares)		0
Surrender of stock in conjunction with net working capital settlement					0
Issuance of stock in conjunction with acquisition			0
Issuance of stock in conjunction with acquisition (in shares)		0
Foreign currency translation adjustment	$ (285)			(285)
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	31,449,931	31,450,000