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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income (in dollars)	$ 137,890	$ 107,583	$ 358,935	$ 204,358
Denominator:
Shares used for basic net income per share (in shares)	162,445	165,924	163,029	168,763
Effect of dilutive securities:
Stock options (in shares)	36	80	59	158
RSUs and DSUs (in shares)	2,077	1,896	1,700	1,811
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)	164,558	167,900	164,788	170,732
Basic net income per share (in dollars per share)	$ 0.85	$ 0.65	$ 2.20	$ 1.21
Diluted net income per share (in dollars per share)	$ 0.84	$ 0.64	$ 2.18	$ 1.20