Net Income Per Share - Calculation of Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 75,749	$ 46,196	$ 89,915	$ 117,181	$ 114,612	$ 109,798	$ 211,860	$ 341,591
Basic:
Weighted average shares (in shares)	112,809			115,181			112,953	116,203
Diluted:
Weighted average shares (in shares)	112,809			115,181			112,953	116,203
Dilutive effect of potential common shares (in shares)	546			687			491	731
Diluted weighted average shares (in shares)	113,355			115,868			113,444	116,934
Net income per share:
Basic (in usd per share)	$ 0.67			$ 1.02			$ 1.88	$ 2.94
Diluted (in usd per share)	$ 0.67			$ 1.01			$ 1.87	$ 2.92