Consolidated Statements of Changes in Stockholder's Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Earnings (Loss)	Accumulated Deficit	Total
Beginning balance at Dec. 31, 2014	$ 43	$ 230,263	$ (154)	$ (189,453)	$ 40,699
Beginning balance (in shares) at Dec. 31, 2014	42,974,463
Increase (Decrease) in Stockholders' Equity
Share-based compensation		4,090			4,090
Issuance of employee stock purchase plan shares		930			930
Issuance of employee stock purchase plan shares (in shares)	98,986
Exercise of stock options		937			937
Exercise of stock options (in shares)	205,640
Equity issued on conversion of convertible notes	$ 6	27,083			27,089
Equity issued on conversion of convertible notes (in shares)	5,693,062
Exercise of warrants		652			652
Exercise of warrants (in shares)	32,523
Net earnings				13,944	13,944
Other comprehensive loss			(334)		(334)
Unrealized (loss) gain on marketable securities, net of tax					(334)
Ending balance at Dec. 31, 2015	$ 49	263,955	(488)	(175,509)	88,007
Ending balance (in shares) at Dec. 31, 2015	49,004,674
Increase (Decrease) in Stockholders' Equity
Share-based compensation		5,926			5,926
Issuance of employee stock purchase plan shares		1,494			1,494
Issuance of employee stock purchase plan shares (in shares)	109,244
Exercise of stock options		557			557
Exercise of stock options (in shares)	85,694
Equity issued on conversion of convertible notes	$ 1	4,161			4,162
Equity issued on conversion of convertible notes (in shares)	771,655
Net earnings				91,221	91,221
Other comprehensive loss					354
Unrealized (loss) gain on marketable securities, net of tax			354		354
Other		34			34
Ending balance at Dec. 31, 2016	$ 50	276,127	(134)	(84,288)	191,755
Ending balance (in shares) at Dec. 31, 2016	49,971,267
Increase (Decrease) in Stockholders' Equity
Cumulative-effect of adoption of ASU 2016-09		211		181	392
Adjusted Balance	$ 50	276,338	(134)	(84,107)	192,147
Share-based compensation		8,433			8,433
Issuance of employee stock purchase plan shares		1,888			1,888
Issuance of employee stock purchase plan shares (in shares)	71,256
Exercise of stock options		3,793			3,793
Exercise of stock options (in shares)	407,477
Equity issued on conversion of convertible notes	$ 1	4,547			4,548
Equity issued on conversion of convertible notes (in shares)	864,850
Net earnings				57,284	57,284
Other comprehensive loss					(613)
Unrealized (loss) gain on marketable securities, net of tax			(613)		(613)
Ending balance at Dec. 31, 2017	$ 51	$ 294,999	$ (747)	$ (26,823)	$ 267,480
Ending balance (in shares) at Dec. 31, 2017	51,314,850