Condensed Consolidated Statements of Changes in Stockholder's Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Earnings (Loss)	Retained Earnings (Accumulated Deficit)
Balance (in shares) at Dec. 31, 2017		51,314,850
Balance at Dec. 31, 2017	$ 267,480	$ 51	$ 294,999	$ (747)	$ (26,823)
Increase (Decrease) in Stockholders' Equity
Share-based compensation	2,635		2,635
Exercise of stock options (in shares)		319,141
Exercise of stock options	2,858	$ 1	2,857
Equity component of convertible notes, 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	26,352				26,352
Unrealized gain (loss) on marketable securities, net of tax	(1,544)			(1,544)
Balance (in shares) at Mar. 31, 2018		51,633,991
Balance at Mar. 31, 2018	351,869	$ 52	352,257	(2,291)	1,851
Balance (in shares) at Dec. 31, 2017		51,314,850
Balance at Dec. 31, 2017	267,480	$ 51	294,999	(747)	(26,823)
Increase (Decrease) in Stockholders' Equity
Net earnings	85,100
Unrealized gain (loss) on marketable securities, net of tax	(3,364)
Balance (in shares) at Sep. 30, 2018		52,257,013
Balance at Sep. 30, 2018	421,936	$ 52	365,396	(4,111)	60,599
Balance (in shares) at Mar. 31, 2018		51,633,991
Balance at Mar. 31, 2018	351,869	$ 52	352,257	(2,291)	1,851
Increase (Decrease) in Stockholders' Equity
Share-based compensation	3,068		3,068
Issuance of ESPP shares (in shares)		34,676
Issuance of ESPP shares	1,184		1,184
Exercise of stock options (in shares)		510,667
Exercise of stock options	5,462		5,462
Net earnings	30,737				30,737
Unrealized gain (loss) on marketable securities, net of tax	(1,828)			(1,828)
Balance (in shares) at Jun. 30, 2018		52,179,334
Balance at Jun. 30, 2018	390,492	$ 52	361,971	(4,119)	32,588
Increase (Decrease) in Stockholders' Equity
Share-based compensation	2,597		2,597
Exercise of stock options (in shares)		77,679
Exercise of stock options	828		828
Net earnings	28,011				28,011
Unrealized gain (loss) on marketable securities, net of tax	8			8
Balance (in shares) at Sep. 30, 2018		52,257,013
Balance at Sep. 30, 2018	421,936	$ 52	365,396	(4,111)	60,599
Balance (in shares) at Dec. 31, 2018		52,316,583
Balance at Dec. 31, 2018	453,023	$ 52	369,637	(3,158)	86,492
Increase (Decrease) in Stockholders' Equity
Share-based compensation	3,287		3,287
Exercise of stock options (in shares)		57,665
Exercise of stock options	783		783
Net earnings	18,340				18,340
Unrealized gain (loss) on marketable securities, net of tax	4,585			4,585
Balance (in shares) at Mar. 31, 2019		52,374,248
Balance at Mar. 31, 2019	480,018	$ 52	373,707	1,427	104,832
Balance (in shares) at Dec. 31, 2018		52,316,583
Balance at Dec. 31, 2018	453,023	$ 52	369,637	(3,158)	86,492
Increase (Decrease) in Stockholders' Equity
Net earnings	79,927
Unrealized gain (loss) on marketable securities, net of tax	10,419
Balance (in shares) at Sep. 30, 2019		52,462,936
Balance at Sep. 30, 2019	557,257	$ 52	383,525	7,261	166,419
Balance (in shares) at Mar. 31, 2019		52,374,248
Balance at Mar. 31, 2019	480,018	$ 52	373,707	1,427	104,832
Increase (Decrease) in Stockholders' Equity
Share-based compensation	4,022		4,022
Issuance of ESPP shares (in shares)		48,950
Issuance of ESPP shares	1,377		1,377
Exercise of stock options (in shares)		25,838
Exercise of stock options	263		263
Net earnings	32,727				32,727
Unrealized gain (loss) on marketable securities, net of tax	4,497			4,497
Balance (in shares) at Jun. 30, 2019		52,449,036
Balance at Jun. 30, 2019	522,904	$ 52	379,369	5,924	137,559
Increase (Decrease) in Stockholders' Equity
Share-based compensation	3,914		3,914
Exercise of stock options (in shares)		13,900
Exercise of stock options	242		242
Net earnings	28,860				28,860
Unrealized gain (loss) on marketable securities, net of tax	1,337			1,337
Balance (in shares) at Sep. 30, 2019		52,462,936
Balance at Sep. 30, 2019	$ 557,257	$ 52	$ 383,525	$ 7,261	$ 166,419