Equity - Statement of Stockholders' Equity (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	$ 412,461	$ 408,374	$ 377,064	$ 374,512	$ 408,374	$ 374,512
Net income (loss)	6,348	2,494	(8,302)	(567)	8,842	(8,869)
Other comprehensive income (loss), net of tax	(24)	(19)	(130)	153
Share-based compensation expense	4,367	3,237	2,974	3,646
Net issuance under employee stock plans	583	(1,625)	755	(680)
Extinguishment of equity component of repurchased/exchanged 2023 Notes			(80)
Equity component of Notes			33,363
Purchase of capped calls			(10,313)
Balance at the end of the period	423,735	412,461	395,331	377,064	423,735	395,331
Common Stock
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	$ 502	$ 497	$ 494	$ 490	$ 497	$ 490
Balance (in shares)	50,183	49,724	49,428	48,994	49,724	48,994
Net issuance under employee stock plans	$ 1	$ 5	$ 3	$ 4
Net issuance under employee stock plans (in shares)	166	459	191	434
Balance at the end of the period	$ 503	$ 502	$ 497	$ 494	$ 503	$ 497
Balance (in shares)	50,349	50,183	49,619	49,428	50,349	49,619
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	$ 1,114,959	$ 1,113,352	$ 1,074,020	$ 1,071,058	$ 1,113,352	$ 1,071,058
Share-based compensation expense	4,367	3,237	2,974	3,646
Net issuance under employee stock plans	582	(1,630)	752	(684)
Extinguishment of equity component of repurchased/exchanged 2023 Notes			(80)
Equity component of Notes			33,363
Purchase of capped calls			(10,313)
Balance at the end of the period	1,119,908	1,114,959	1,100,716	1,074,020	1,119,908	1,100,716
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	(704,827)	(707,321)	(699,497)	(698,930)	(707,321)	(698,930)
Net income (loss)	6,348	2,494	(8,302)	(567)
Balance at the end of the period	(698,479)	(704,827)	(707,799)	(699,497)	(698,479)	(707,799)
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	1,827	1,846	2,047	1,894	1,846	1,894
Other comprehensive income (loss), net of tax	(24)	(19)	(130)	153
Balance at the end of the period	$ 1,803	$ 1,827	$ 1,917	$ 2,047	$ 1,803	$ 1,917