Equity - Statement of Stockholders' Equity (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	$ 377,064	$ 374,512	$ 421,798	$ 437,775	$ 374,512	$ 437,775
Net loss	(8,302)	(567)	(15,565)	(18,530)	(8,869)	(34,095)
Other comprehensive income (loss), net of tax	(130)	153	20	38
Share-based compensation expense	2,974	3,646	4,588	3,157
Net issuance under employee stock plans	755	(680)	185	(642)
Extinguishment of equity component of repurchased 2023 Notes	(80)
Equity component of 2027 Notes	33,363
Purchase of capped calls	(10,313)
Balance at the end of the period	395,331	377,064	411,026	421,798	395,331	411,026
Common Stock
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	$ 494	$ 490	$ 487	$ 485	$ 490	$ 485
Balance (in shares)	49,428	48,994	48,675	48,547	48,994	48,547
Net issuance under employee stock plans	$ 3	$ 4	$ 3	$ 2
Net issuance under employee stock plans (in shares)	191	434	296	128
Balance at the end of the period	$ 497	$ 494	$ 490	$ 487	$ 497	$ 490
Balance (in shares)	49,619	49,428	48,971	48,675	49,619	48,971
Treasury Stock
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period				$ (5,872)		$ (5,872)
Balance (in shares)				523		523
Net issuance under employee stock plans				$ 5,872
Net issuance under employee stock plans (in shares)				(523)
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	$ 1,074,020	$ 1,071,058	$ 1,058,179	$ 1,061,325	$ 1,071,058	$ 1,061,325
Share-based compensation expense	2,974	3,646	4,588	3,157
Net issuance under employee stock plans	752	(684)	182	(6,303)
Extinguishment of equity component of repurchased 2023 Notes	(80)
Equity component of 2027 Notes	33,363
Purchase of capped calls	(10,313)
Balance at the end of the period	1,100,716	1,074,020	1,062,949	1,058,179	1,100,716	1,062,949
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	(699,497)	(698,930)	(638,726)	(619,983)	(698,930)	(619,983)
Net loss	(8,302)	(567)	(15,565)	(18,530)
Net issuance under employee stock plans				(213)
Balance at the end of the period	(707,799)	(699,497)	(654,291)	(638,726)	(707,799)	(654,291)
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	2,047	1,894	1,858	1,820	1,894	1,820
Other comprehensive income (loss), net of tax	(130)	153	20	38
Balance at the end of the period	$ 1,917	$ 2,047	$ 1,878	$ 1,858	$ 1,917	$ 1,878