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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net income (in dollars)	$ 113,915	$ 43,061	$ 221,045	$ 96,775
Denominator:
Shares used for basic net income per share (in shares)	163,407	170,250	163,322	170,183
Effect of dilutive securities:
Stock options (in shares)	92	268	71	205
RSUs and DSUs (in shares)	1,520	1,789	1,510	1,768
Convertible senior notes (in shares)	0	0	0	0
Warrants related to issuance of convertible senior notes (in shares)	0	0	0	0
Shares used for diluted net income per share (in shares)	165,019	172,307	164,903	172,156
Basic net income per share (in dollars per share)	$ 0.70	$ 0.25	$ 1.35	$ 0.57
Diluted net income per share (in dollars per share)	$ 0.69	$ 0.25	$ 1.34	$ 0.56