Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Assets [Abstract]
Cash and due from banks	$ 546,575	$ 620,846	$ 481,510
Interest-bearing cash and cash equivalents	2,220,640	1,916,651	1,831,162
Trading securities	677,156	337,628	279,539
Investment securities	519,402	546,145	576,047
Available for sale securities	8,437,291	8,676,829	8,886,036
Fair value option securities	441,714	77,046	418,887
Restricted equity securities	283,936	307,240	314,590
Residential mortgage loans held for sale	248,707	301,897	332,040
Loans	16,991,906	16,989,660	16,022,566
Allowance for loan losses	(248,710)	(246,159)	(233,156)
Loans, net of allowance	16,743,196	16,743,501	15,789,410
Premises and equipment, net	325,546	325,849	311,161
Receivables	394,394	772,952	167,209
Goodwill	445,738	448,899	383,789
Intangible assets, net	42,556	46,931	44,944
Mortgage servicing rights	249,403	247,073	196,055
Real estate and other repossessed assets, net of allowance	42,726	44,287	29,896
Derivative contracts, net	304,727	689,872	790,146
Cash surrender value of bank-owned life insurance	310,537	308,430	305,510
Receivable on unsettled securities sales	9,921	7,188	5,640
Other assets	384,767	353,017	270,374
Total assets	32,628,932	32,772,281	31,413,945
Deposits [Abstract]
Noninterest-bearing demand deposits	9,506,573	9,235,720	7,950,675
Interest-bearing deposits: [Abstract]
Transaction	10,359,214	10,865,105	9,709,766
Savings	465,724	425,470	416,505
Time	2,243,848	2,221,800	2,341,374
Total deposits	22,575,359	22,748,095	20,418,320
Funds purchased	47,629	57,929	62,755
Repurchase agreements	508,352	668,661	630,101
Other borrowings	5,238,947	4,846,072	5,633,862
Subordinated debentures	144,649	144,640	226,385
Accrued interest, taxes and expense	140,235	146,704	148,711
Derivative contracts, net	276,422	664,531	705,578
Due on unsettled securities purchases	137,069	6,508	19,508
Other liabilities	189,376	182,784	212,460
Total liabilities	29,258,038	29,465,924	28,057,680
Shareholders' equity: [Abstract]
Common stock	4	4	4
Capital surplus	1,009,360	1,006,535	987,046
Retained earnings	2,883,042	2,823,334	2,718,301
Treasury stock	(545,441)	(544,052)	(476,905)
Accumulated other comprehensive income (loss)	(5,221)	(10,967)	93,109
Total shareholders’ equity	3,341,744	3,274,854	3,321,555
Non-controlling interests	29,150	31,503	34,710
Total equity	3,370,894	3,306,357	3,356,265
Total liabilities and equity	$ 32,628,932	$ 32,772,281	$ 31,413,945