Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets [Abstract]
Cash and due from banks	$ 620,846	$ 573,699
Interest-bearing cash and cash equivalents	1,916,651	2,069,900
Trading securities	337,628	122,404
Investment securities	546,145	597,836
Available for sale securities	8,676,829	9,042,733
Fair value option securities	77,046	444,217
Restricted equity securities	307,240	273,684
Residential mortgage loans held for sale	301,897	308,439
Loans	16,989,660	15,941,154
Allowance for loan losses	(246,159)	(225,524)
Loans, net of allowance	16,743,501	15,715,630
Premises and equipment, net	325,849	306,490
Receivables	772,952	163,480
Goodwill	448,899	385,461
Intangible assets, net	46,931	43,909
Mortgage servicing rights	247,073	218,605
Real estate and other repossessed assets, net of allowance	44,287	30,731
Derivative contracts	689,872	586,270
Cash surrender value of bank-owned life insurance	308,430	303,335
Receivable on unsettled available for sale securities sales	7,188	40,193
Other assets	353,017	249,112
Total assets	32,772,281	31,476,128
Deposits [Abstract]
Noninterest-bearing demand deposits	9,235,720	8,296,888
Interest-bearing Deposit Liabilities [Abstract]
Transaction	10,865,105	9,998,954
Savings	425,470	386,252
Time	2,221,800	2,406,064
Total deposits	22,748,095	21,088,158
Funds purchased	57,929	491,192
Repurchase agreements	668,661	722,444
Other borrowings	4,846,072	4,837,879
Subordinated debentures	144,640	226,350
Accrued interest, taxes and expense	146,704	119,584
Derivative contracts	664,531	581,701
Due on unsettled available for sale securities purchases	6,508	16,897
Other liabilities	182,784	124,284
Total liabilities	29,465,924	28,208,489
Shareholders' equity: [Abstract]
Common stock	4	4
Capital surplus	1,006,535	982,009
Retained earnings	2,823,334	2,704,121
Treasury stock	(544,052)	(477,165)
Accumulated other comprehensive income (loss)	(10,967)	21,587
Total shareholders’ equity	3,274,854	3,230,556
Non-controlling interests	31,503	37,083
Total equity	3,306,357	3,267,639
Total liabilities and equity	$ 32,772,281	$ 31,476,128