Consolidated Statements of Changes in Stockholder's Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Earnings (Loss)	Retained Earnings (Accumulated Deficit)	Total
Beginning balance at Dec. 31, 2015	$ 49	$ 263,955	$ (488)	$ (175,509)	$ 88,007
Beginning 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
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 | 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
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
Increase (Decrease) in Stockholders' Equity
Cumulative-effect of adoption of ASU | ASU 2014-09				2,322	2,322
Adjusted Balance	$ 51	294,999	(747)	(24,501)	269,802
Share-based compensation		11,291			11,291
Issuance of employee stock purchase plan shares		2,209			2,209
Issuance of employee stock purchase plan shares (in shares)	71,250
Exercise of stock options	$ 1	9,372			9,373
Exercise of stock options (in shares)	930,483
Equity component of convertible notes issuance, net of tax		56,215			56,215
Purchases of convertible note hedges, net of tax		(70,137)			(70,137)
Issuance of warrants		65,688			65,688
Net earnings				110,993	110,993
Unrealized (loss) gain on marketable securities, net of tax			(2,411)		(2,411)
Ending balance at Dec. 31, 2018	$ 52	$ 369,637	$ (3,158)	$ 86,492	$ 453,023
Ending balance (in shares) at Dec. 31, 2018	52,316,583