Consolidated Statement of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	$0.001 Par Value Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Total
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standard (ASC 606), net of tax | ASC 606 [Member]	$ 0	$ 0		$ 0	$ (32,527)	$ (32,527)
Balance at Dec. 31, 2017	50	618,416	$ (39,497)	(3,698)	337,074	912,345
Balance (ASC 606 [Member]) at Dec. 31, 2017	$ 50	618,416	$ (39,497)	(3,698)	304,547	$ 879,818
Balance (in shares) at Dec. 31, 2017	50,619,808		(1,214,443)			49,405,365
Balance (in shares) (ASC 606 [Member]) at Dec. 31, 2017	50,619,808		(1,214,443)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee equity plans activity	$ 0	6,068		0	0	$ 6,068
Employee equity plans activity (in shares)	406,170
Treasury stock		0	$ (145)	0	0	(145)
Treasury stock (in shares)			(2,843)
Net income (loss)		0		0	(4,908)	(4,908)
Foreign currency translation, net of tax		0		447	0	447
Balance at Mar. 31, 2018	$ 50	$ 624,484	$ (39,642)	$ (3,251)	$ 299,639	$ 881,280
Balance (in shares) at Mar. 31, 2018	51,025,978		(1,217,286)			49,808,692