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, 2015	12,980,807
Balance at Dec. 31, 2015	$ 13	$ 79,782	$ (29,672)	$ (89)	$ 50,034
Deferred tax relating to adoption of ASU 2016-09 at Dec. 31, 2015			49		49
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			$ 9,342
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
Balance at Dec. 31, 2016	$ 14	88,114	(27,046)	(72)	61,010
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
Issuance of common stock for employee purchase plan (in shares)	64,511
Issuance of common stock for employee purchase plan	$ 1	1,680			$ 1,680
Exercise of stock options (in shares)	271,902				271,902
Exercise of stock options		2,718			$ 2,718
Issuance of common stock in settlement of restricted and performance stock units, net of shares withheld for employee taxes, and stock awards (in shares)	154,466
Issuance of common stock in settlement of restricted and performance stock units, net of shares withheld for employee taxes, and stock awards		(3,128)			(3,128)
Stock-based compensation expense		7,157			7,157
Net income (loss)			(30,770)		(30,770)
Net change in unrealized loss on available-for-sale investments				23	23
Adjustment to opening balance for ASC 606 adoption at Dec. 31, 2017			3,813		$ 3,813
Balance (in shares) at Dec. 31, 2018	13,968,852				13,968,852
Balance at Dec. 31, 2018	$ 14	$ 70,451	$ (24,010)	$ (69)	$ 46,386