Parent Company Only Condensed Financial Information - Condensed Statements of Income (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
Condensed Income Statements, Captions [Line Items]
Interest income	$ 542,897	$ 513,313	$ 481,301	$ 432,398	$ 405,016	$ 385,271	$ 353,927	$ 320,926	$ 1,969,909		$ 1,465,140		$ 1,193,396
Interest expense	(28,437)	(20,091)	(14,858)	(12,535)	(11,310)	(11,297)	(11,231)	(10,933)	(75,921)		(44,771)		(42,873)
Gains on equity warrant assets, net									89,142		54,555		37,892	[1]
Gains on investment securities, net									88,094		64,603		51,740
Fund management fees									23,016		21,214		19,195
Income tax expense	(105,000)	(95,308)	(77,287)	(73,966)	(135,051)	(97,351)	(71,656)	(51,405)	(351,561)	[2]	(355,463)	[2]	(250,333)
Net income available to common stockholders	$ 266,264	$ 274,817	$ 237,798	$ 194,961	$ 117,210	$ 148,620	$ 123,193	$ 101,483	973,840	[2]	490,506	[2]	382,685
Parent Company
Condensed Income Statements, Captions [Line Items]
Interest income									3,307		2,077		690
Interest expense									(32,037)		(34,932)		(35,316)
Dividend income from subsidiary									140,000		90,000		40,000
Gains on equity warrant assets, net									89,142		54,555		37,892
Gains on investment securities, net									13,546		37,132		20,644
Fund management fees									26,388		24,613		21,913
General and administrative expenses									(70,976)		(63,077)		(55,139)
Income tax expense									(14,383)		10,367		423
Loss before net income of subsidiaries									154,987		120,735		31,107
Net income available to common stockholders									973,840		490,506		382,685
Parent Company | Bank Subsidiaries
Condensed Income Statements, Captions [Line Items]
Loss before net income of subsidiaries									933,641		446,769		379,629
Equity in undistributed net income of subsidiary									793,641		356,769		339,629
Parent Company | Nonbank Subsidiaries
Condensed Income Statements, Captions [Line Items]
Loss before net income of subsidiaries									25,212		13,002		11,949
Equity in undistributed net income of subsidiary									$ 25,212		$ 13,002		$ 11,949

[1] Our consolidated statements of income for the year ended December 31, 2016 was modified from prior periods’ presentation to conform to the current period's presentation, which reflects a new line item to separately disclose net gains on equity warrant assets. In prior periods, net gains on equity warrant assets were reported as a component of net gains on derivative instruments. We removed the line item "gains on derivative instruments, net" and reclassified all other gains on derivative instruments, net to other noninterest income.

[2] 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.