Stockholders' Equity and EPS - Reconciliation of Basic EPS to Diluted EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income available to common stockholders	$ 228,935	$ 317,987	$ 361,188	$ 606,719
Denominator:
Weighted average common shares outstanding-basic (in shares)	51,581	51,955	51,573	52,269
Weighted average common shares outstanding—diluted (in shares)	51,795	52,336	51,848	52,715
Earnings per common share:
Basic (dollars per share)	$ 4.44	$ 6.12	$ 7.00	$ 11.61
Diluted (dollars per share)	$ 4.42	$ 6.08	$ 6.97	$ 11.51
Stock options and ESPP
Denominator:
Weighted average effect of dilutive securities (in shares)	114	235	140	254
Restricted stock units and awards
Denominator:
Weighted average effect of dilutive securities (in shares)	100	146	135	192