Net Income per Share - Schedule of Components Used in Diluted and Basic Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income (in dollars)	$ 53,714	$ 74,583
Denominator:
Shares used for basic net income per share (in shares)	170,116	173,158
Effect of dilutive securities:
Stock options (in shares)	142	360
RSUs and DSUs (in shares)	1,746	1,653
Convertible senior notes (in shares)	0	0
Warrants related to issuance of convertible senior notes (in shares)	0	0
Shares used for diluted net income per share (in shares)	172,004	175,171
Basic net income per share (in dollars per share)	$ 0.32	$ 0.43
Diluted net income per share (in dollars per share)	$ 0.31	$ 0.43