Equity - Statement of Stockholders' Equity (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	$ 437,775	$ 840,093
Net loss	(18,530)	(15,827)
Other comprehensive income, net of tax	38	24
Share-based compensation expense	3,157	4,537
Net issuance under employee stock plans	(642)	(426)
Purchases of common stock		(444)
Balance at the end of the period	421,798	827,957
Common Stock
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	$ 485	$ 482
Balance (in shares)	48,547	48,229
Net issuance under employee stock plans	$ 2	$ 5
Net issuance under employee stock plans (in shares)	128	462
Balance at the end of the period	$ 487	$ 487
Balance (in shares)	48,675	48,691
Treasury Stock
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	$ (5,872)	$ (1,284)
Balance (in shares)	523	85
Net issuance under employee stock plans	$ 5,872	$ 1,728
Net issuance under employee stock plans (in shares)	(523)	(115)
Purchases of common stock		$ (444)
Purchase of common stock (in shares)		30
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	$ 1,061,325	$ 1,051,953
Share-based compensation expense	3,157	4,537
Net issuance under employee stock plans	(6,303)	(2,159)
Balance at the end of the period	1,058,179	1,054,331
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	(619,983)	(212,870)
Net loss	(18,530)	(15,827)
Net issuance under employee stock plans	(213)
Balance at the end of the period	(638,726)	(228,697)
Accumulated Other Comprehensive Income
Increase (Decrease) in Stockholders' Equity
Balance at the beginning of the period	1,820	1,812
Other comprehensive income, net of tax	38	24
Balance at the end of the period	$ 1,858	$ 1,836