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, 2019	Mar. 31, 2018
Numerator:
Net income (in dollars)	$ 107,130	$ 53,714
Denominator:
Shares used for basic net income per share (in shares)	163,236	170,116
Effect of dilutive securities:
Stock options (in shares)	49	142
RSUs and DSUs (in shares)	1,502	1,746
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)	164,787	172,004
Basic net income per share (in dollars per share)	$ 0.66	$ 0.32
Diluted net income per share (in dollars per share)	$ 0.65	$ 0.31