Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings (Deficit) [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2016	$ 134,161	$ 698	$ 119,733	$ 187,242	$ (173,512)
Beginning Balance, Shares at Dec. 31, 2016		58,801,104			10,987,362
Net income	95,128			95,128
Employee stock plans	393	$ 2	391
Employee stock plans, Shares		33,228
Shares withheld for taxes on awards	(3,619)	$ (2)	(3,617)
Shares withheld for taxes on awards, Shares		(58,470)
Stock-based compensation	5,187		5,187
Stock-based compensation, Shares		80,998
Ending Balance at Dec. 31, 2017	231,250	$ 698	121,694	282,370	$ (173,512)
Ending Balance, Shares at Dec. 31, 2017		58,856,860			10,987,362
Net income	134,572			134,572
Employee stock plans	882	$ 1	881
Employee stock plans, Shares		63,448
Shares withheld for taxes on awards	(4,695)		(4,695)
Shares withheld for taxes on awards, Shares		(13,028)
Stock-based compensation	6,345	$ 1	6,344
Stock-based compensation, Shares		103,694
Repurchases of common stock	(25,391)				$ (25,391)
Repurchases of common stock, Shares		(459,321)			459,321
Ending Balance at Dec. 31, 2018	342,963	$ 700	124,224	416,942	$ (198,903)
Ending Balance, Shares at Dec. 31, 2018		58,551,653			11,446,683
Net income	144,738			144,738
Employee stock plans	1,089	$ 1	1,088
Employee stock plans, Shares		77,141
Shares withheld for taxes on awards	(8,245)		(8,245)
Shares withheld for taxes on awards, Shares		(108,378)
Stock-based compensation	6,930	$ 1	6,929
Stock-based compensation, Shares		220,364
Repurchases of common stock	(38,300)				$ (38,300)
Repurchases of common stock, Shares		(500,059)			500,059
Ending Balance at Dec. 31, 2019	$ 449,175	$ 702	$ 123,996	$ 561,680	$ (237,203)
Ending Balance, Shares at Dec. 31, 2019		58,240,721			11,946,742