Income Taxes - Components of Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Current provision:
Federal									$ 249,358		$ 263,231		$ 195,249
State									123,264		67,046		59,319
Deferred expense (benefit):
Federal									(11,777)		24,654		(3,560)
State									(9,284)		532		(675)
Income tax expense	$ 105,000	$ 95,308	$ 77,287	$ 73,966	$ 135,051	$ 97,351	$ 71,656	$ 51,405	$ 351,561	[1]	$ 355,463	[1]	$ 250,333

[1] Included in income tax expense, net income available to common stockholders, earnings per common share-basic and earnings for common share-diluted, for the years ended December 31, 2018 and 2017, are tax benefits recognized associated with the adoption of Accounting Standards Update ("ASU") 2016-09, Improvements to Employee Share-Based Payment Accounting in the first quarter of 2017. This guidance was adopted on a prospective basis with no change to prior period amounts.