Net Income Per Share - Calculation of Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net income	$ 149,213	$ 110,598	$ 46,196	$ 89,915	$ 259,811	$ 136,111
Basic:
Weighted average shares (in shares)	110,861		112,865		111,141	113,026
Diluted:
Weighted average shares (in shares)	110,861		112,865		111,141	113,026
Dilutive effect of potential common shares (in shares)	1,028		256		1,050	463
Diluted weighted average shares (in shares)	111,889		113,121		112,191	113,489
Net income per share:
Basic (in usd per share)	$ 1.35		$ 0.41		$ 2.34	$ 1.20
Diluted (in usd per share)	$ 1.33		$ 0.41		$ 2.32	$ 1.20