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, 2017	$ 231,250	$ 698	$ 121,694	$ 282,370	$ (173,512)
Beginning Balance, Shares at Dec. 31, 2017		58,856,860			10,987,362
Net income	37,110			37,110
Employee stock purchase and option plans	195	$ 0	195
Employee stock purchase and option plans, Shares		26,832
Shares withheld for taxes on share-based payment awards	(3,782)	$ 0	(3,782)
Shares withheld for taxes on share-based payment awards, Shares		(13,028)
Stock-based compensation	2,296	$ 1	2,295
Stock-based compensation, Shares		80,988
Shares repurchased under our publicly announced share repurchase programs	(5,210)				$ (5,210)
Shares repurchased under our publicly announced share repurchase programs, Shares		(100,044)			100,044
Ending Balance at Mar. 31, 2018	261,859	$ 699	120,402	319,480	$ (178,722)
Ending Balance, Shares at Mar. 31, 2018		58,851,608			11,087,406
Beginning Balance at Dec. 31, 2018	342,963	$ 700	124,224	416,942	$ (198,903)
Beginning Balance, Shares at Dec. 31, 2018		58,551,653			11,446,683
Net income	31,555			31,555
Employee stock purchase and option plans	302	$ 0	302
Employee stock purchase and option plans, Shares		24,472
Shares withheld for taxes on share-based payment awards	(5,727)	$ 0	(5,727)
Shares withheld for taxes on share-based payment awards, Shares		(74,010)
Stock-based compensation	2,794	$ 1	2,793
Stock-based compensation, Shares		160,359
Shares repurchased under our publicly announced share repurchase programs	(8,730)				$ (8,730)
Shares repurchased under our publicly announced share repurchase programs, Shares		(124,989)			124,989
Ending Balance at Mar. 31, 2019	$ 363,157	$ 701	$ 121,592	$ 448,497	$ (207,633)
Ending Balance, Shares at Mar. 31, 2019		58,537,485			11,571,672