Loans, Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	$ 278,335	$ 274,264
Charge offs	(11,854)	(86,439)
Recoveries	6,191	21,510
Net charge offs	(5,663)	(64,929)
Provision for loan losses	10,000	69,000
Balance at end of period	282,672	278,335
Allowance for loan losses:
Individually evaluated for impairment	28,365	24,103
Collectively evaluated for impairment	254,307	254,232
Balance at end of period	282,672	278,335
Loans:
Individually evaluated for impairment	199,459	214,409
Collectively evaluated for impairment	19,948,224	19,840,307
Total loans	20,147,683	20,054,716
Commercial and industrial
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	140,126	129,959
Charge offs	(9,359)	(71,016)
Recoveries	4,991	14,543
Net charge offs	(4,368)	(56,473)
Provision for loan losses	10,509	66,640
Balance at end of period	146,267	140,126
Allowance for loan losses:
Individually evaluated for impairment	25,915	20,836
Collectively evaluated for impairment	120,352	119,290
Balance at end of period	146,267	140,126
Loans:
Individually evaluated for impairment	162,788	180,965
Collectively evaluated for impairment	6,137,858	6,308,049
Total loans	6,300,646	6,489,014
Commercial real estate — owner occupied
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	14,034	18,680
Charge offs	(5)	(512)
Recoveries	24	74
Net charge offs	19	(438)
Provision for loan losses	(2,841)	(4,208)
Balance at end of period	11,212	14,034
Allowance for loan losses:
Individually evaluated for impairment	1,541	0
Collectively evaluated for impairment	9,671	14,034
Balance at end of period	11,212	14,034
Loans:
Individually evaluated for impairment	17,098	8,439
Collectively evaluated for impairment	861,293	889,285
Total loans	878,391	897,724
Commercial real estate — investor
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	45,285	43,018
Charge offs	(633)	(1,504)
Recoveries	119	1,624
Net charge offs	(514)	120
Provision for loan losses	(3,406)	2,147
Balance at end of period	41,365	45,285
Allowance for loan losses:
Individually evaluated for impairment	99	3,117
Collectively evaluated for impairment	41,266	42,168
Balance at end of period	41,365	45,285
Loans:
Individually evaluated for impairment	7,615	17,322
Collectively evaluated for impairment	3,407,740	3,557,410
Total loans	3,415,355	3,574,732
Real estate construction
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	26,932	25,266
Charge offs	(23)	(558)
Recoveries	34	203
Net charge offs	11	(355)
Provision for loan losses	1,825	2,021
Balance at end of period	28,768	26,932
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	28,768	26,932
Balance at end of period	28,768	26,932
Loans:
Individually evaluated for impairment	225	0
Collectively evaluated for impairment	1,552,980	1,432,497
Total loans	1,553,205	1,432,497
Residential mortgage
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	27,046	28,261
Charge offs	(297)	(4,332)
Recoveries	169	755
Net charge offs	(128)	(3,577)
Provision for loan losses	3,370	2,362
Balance at end of period	30,288	27,046
Allowance for loan losses:
Individually evaluated for impairment	810	147
Collectively evaluated for impairment	29,478	26,899
Balance at end of period	30,288	27,046
Loans:
Individually evaluated for impairment	11,086	7,033
Collectively evaluated for impairment	6,704,196	6,325,294
Total loans	6,715,282	6,332,327
Home equity
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	20,364	23,555
Charge offs	(509)	(4,686)
Recoveries	682	3,491
Net charge offs	173	(1,195)
Provision for loan losses	(223)	(1,996)
Balance at end of period	20,314	20,364
Allowance for loan losses:
Individually evaluated for impairment	0	3
Collectively evaluated for impairment	20,314	20,361
Balance at end of period	20,314	20,364
Loans:
Individually evaluated for impairment	647	650
Collectively evaluated for impairment	911,322	933,793
Total loans	911,969	934,443
Other consumer
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	4,548	5,525
Charge offs	(1,028)	(3,831)
Recoveries	172	820
Net charge offs	(856)	(3,011)
Provision for loan losses	766	2,034
Balance at end of period	4,458	4,548
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	4,458	4,548
Balance at end of period	4,458	4,548
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	372,835	393,979
Total loans	$ 372,835	$ 393,979