CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balances at beginning of period at Dec. 31, 2017	$ (268,570)	$ 423	$ 1,035,808	$ (1,284,703)	$ (17,672)	$ (2,426)
Balances at beginning of period (in shares) at Dec. 31, 2017		42,339			(983)
Cumulative-effect adjustment due to adoption of ASU No. 2016-09	108,367			108,367
Stock issued pursuant to employee stock plans	(643)		(13,084)		$ 12,441
Stock issued pursuant to employee stock plans (in shares)					592
Stock-based compensation	6,258		6,258
Net (loss) income	(10,674)			(10,674)
Other comprehensive income (loss)	(1,341)					(1,341)
Partial retirement of convertible senior notes conversion feature	(74)		(74)
Partial unwind capped call cash receipt	16		16
Balances at end of period at Dec. 31, 2018	(166,661)	$ 423	1,028,924	(1,187,010)	$ (5,231)	(3,767)
Balances at end of period (in shares) at Dec. 31, 2018		42,339			(391)
Stock issued pursuant to employee stock plans	$ (3,270)	$ 7	(8,508)		$ 5,231
Stock issued pursuant to employee stock plans (in shares)	811				391
Stock-based compensation	$ 7,958		7,958
Net (loss) income	7,601			7,601
Other comprehensive income (loss)	(163)					(163)
Partial retirement of convertible senior notes conversion feature	(577)		(577)
Partial unwind capped call cash receipt	27		27
Balances at end of period at Dec. 31, 2019	$ (155,085)	$ 430	1,027,824	(1,179,409)	$ 0	(3,930)
Balances at end of period (in shares) at Dec. 31, 2019	41,948	43,150			0
Stock issued pursuant to employee stock plans	$ (1,818)	$ 12	(1,830)
Stock issued pursuant to employee stock plans (in shares)	1,270
Stock-based compensation	$ 10,664		10,664
Net (loss) income	11,062			11,062
Other comprehensive income (loss)	2,253					2,253
Balances at end of period at Dec. 31, 2020	$ (132,924)	$ 442	$ 1,036,658	$ (1,168,347)	$ 0	$ (1,677)
Balances at end of period (in shares) at Dec. 31, 2020	43,150	44,420			0