Parent Company Financial Information - Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income/(loss) attributable to controlling interest	$ 440,908	$ 545,042	$ 165,515
Adjustments to reconcile net income/(loss) to net cash provided/(used) by operating activities:
Depreciation, amortization, and other	65,239	59,125	70,924
(Gain)/loss on securities	(441)	(212,896)	(109)
Provision/(benefit) for deferred income taxes	14,357	103,557	121,001
Stock-based compensation expense	22,730	23,171	20,627
Net (increase)/decrease in interest receivable and other assets	(116,888)	32,950	240,629
Net (decrease)/increase in interest payable and other liabilities	95,200	(3,980)	(16,877)
Total adjustments	377,921	(322,202)	(205,778)
Net cash provided/(used) by operating activities	830,294	234,305	(28,798)
Securities:
Sales and prepayments	191,681	20,751
Sales and prepayments			936,958
Premises and equipment:
Net cash provided/(used) by investing activities	(2,389,842)	480,372	(1,324,602)
Preferred stock:
Cash dividends	(6,200)	(6,200)	(6,200)
Common stock:
Exercise of stock options	9,665	4,482	6,132
Cash dividends	(171,076)	(138,706)	(79,904)
Repurchase of shares	(134,813)	(104,768)	(5,554)
Term borrowings:
Repayment of term borrowings	(405,562)	(69,025)	(147,413)
Net cash provided/(used) by financing activities	1,421,116	(761,398)	1,767,652
Net increase/(decrease) in cash and cash equivalents	(138,432)	(46,721)	414,252
Cash and cash equivalents at beginning of period	1,405,325	1,452,046	1,037,794
Cash and cash equivalents at end of period	1,266,893	1,405,325	1,452,046
Total interest paid	410,883	307,578	140,373
Total taxes paid	70,505	42,817	54,417
Parent Company
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net income/(loss) attributable to controlling interest	440,908	545,042	165,515
Less undistributed net income/(loss) of subsidiaries	157,572	169,751	(23,541)
Income/(loss) before undistributed net income of subsidiaries	283,336	375,291	189,056
Adjustments to reconcile net income/(loss) to net cash provided/(used) by operating activities:
Depreciation, amortization, and other	(915)	15	15
(Gain)/loss on securities	(317)	(28)	(109)
Provision/(benefit) for deferred income taxes	3,648	3,212	7,727
Stock-based compensation expense	21,909	22,398	19,625
Net (increase)/decrease in interest receivable and other assets	10,170	18,214	8,605
Net (decrease)/increase in interest payable and other liabilities	17,736	(10,702)	13,172
Total adjustments	52,231	33,109	49,035
Net cash provided/(used) by operating activities	335,567	408,400	238,091
Securities:
Sales and prepayments	1,457	65
Sales and prepayments			318
Premises and equipment:
Sales/(purchases)	19	(43)	7
Return on investment in subsidiary	164	1,597	1,871
Cash paid for business combination, net	0	(39,916)	(126,149)
Net cash provided/(used) by investing activities	1,640	(38,297)	(123,953)
Preferred stock:
Cash dividends	(6,200)	(6,200)	(6,200)
Common stock:
Exercise of stock options	9,665	4,482	6,132
Cash dividends	(171,076)	(138,706)	(79,904)
Repurchase of shares	(134,813)	(104,768)	(5,554)
Term borrowings:
Repayment of term borrowings	0	(45,364)	0
Net cash provided/(used) by financing activities	(302,424)	(290,556)	(85,526)
Net increase/(decrease) in cash and cash equivalents	34,783	79,547	28,612
Cash and cash equivalents at beginning of period	334,485	254,938	226,326
Cash and cash equivalents at end of period	369,268	334,485	254,938
Total interest paid	29,169	29,186	17,321
Total taxes paid	$ 43,418	$ 49,056	$ 23,020