Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2014	14,446,950
Balance at Dec. 31, 2014	$ 14	$ 105,721	$ (25,232)	$ 5	$ 80,508
Issuance of common stock for employee purchase plan (in shares)	55,872
Issuance of common stock for employee purchase plan		577			$ 577
Exercise of stock options (in shares)	1,141,904				1,141,904
Exercise of stock options	$ 2	10,500			$ 10,502
Issuance of common stock in settlement of restricted and performance stock units, net of shares withheld for employee taxes, and stock awards (in shares)	154,119
Issuance of common stock in settlement of restricted and performance stock units, net of shares withheld for employee taxes, and stock awards		(1,018)			(1,018)
Repurchase of common stock (in shares)	(2,818,038)
Repurchase of common stock	$ (3)	(40,082)			(40,085)
Stock-based compensation expense		4,084			4,084
Net income (loss)			(4,440)		(4,440)
Net change in unrealized loss on available-for-sale investments				(94)	(94)
Balance (in shares) at Dec. 31, 2015	12,980,807
Balance at Dec. 31, 2015	$ 13	79,782	(29,672)	(89)	50,034
Issuance of common stock for employee purchase plan (in shares)	79,922
Issuance of common stock for employee purchase plan		768			$ 768
Exercise of stock options (in shares)	1,051,138				1,051,138
Exercise of stock options	$ 1	9,342			$ 9,343
Issuance of common stock in settlement of restricted and performance stock units, net of shares withheld for employee taxes, and stock awards (in shares)	116,833
Issuance of common stock in settlement of restricted and performance stock units, net of shares withheld for employee taxes, and stock awards		(618)			(618)
Repurchase of common stock (in shares)	(455,311)
Repurchase of common stock		(4,873)			(4,873)
Stock-based compensation expense		3,713			3,713
Net income (loss)			2,577		2,577
Net change in unrealized loss on available-for-sale investments				17	$ 17
Balance (in shares) at Dec. 31, 2016	13,773,389				13,773,389
Balance at Dec. 31, 2016	$ 14	88,114	(27,046)	(72)	$ 61,010
Deferred tax relating to adoption of ASU 2016-09			49		49
Issuance of common stock for employee purchase plan (in shares)	78,479
Issuance of common stock for employee purchase plan		1,059			$ 1,059
Exercise of stock options (in shares)	488,398				488,398
Exercise of stock options		4,376			$ 4,376
Issuance of common stock in settlement of restricted and performance stock units, net of shares withheld for employee taxes, and stock awards (in shares)	160,309
Issuance of common stock in settlement of restricted and performance stock units, net of shares withheld for employee taxes, and stock awards		(1,469)			(1,469)
Repurchase of common stock (in shares)	(1,022,602)
Repurchase of common stock	$ (1)	(35,165)			(35,166)
Stock-based compensation expense		5,110			5,110
Net income (loss)			29,993		29,993
Net change in unrealized loss on available-for-sale investments				(20)	$ (20)
Balance (in shares) at Dec. 31, 2017	13,477,973				13,477,973
Balance at Dec. 31, 2017	$ 13	$ 62,025	$ 2,947	$ (92)	$ 64,893