Loans, Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 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	(27,230)	(86,439)
Recoveries	8,996	21,510
Net charge offs	(18,234)	(64,929)
Provision for loan losses	21,000	69,000
Balance at end of period	281,101	278,335
Allowance for loan losses:
Individually evaluated	17,826	24,103
Collectively evaluated	22,162	22,380
Total impaired loans	39,988	46,483
Collectively evaluated	241,113	231,852
Balance at end of period	281,101	278,335
Loans:
Individually evaluated	174,086	214,409
Collectively evaluated	135,127	140,751
Total impaired loans	309,213	355,160
Collectively evaluated	20,473,856	19,699,556
Total loans	20,783,069	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	(21,912)	(71,016)
Recoveries	6,498	14,543
Net charge offs	(15,414)	(56,473)
Provision for loan losses	18,295	66,640
Balance at end of period	143,007	140,126
Allowance for loan losses:
Individually evaluated	17,350	20,836
Collectively evaluated	532	781
Total impaired loans	17,882	21,617
Collectively evaluated	125,125	118,509
Balance at end of period	143,007	140,126
Loans:
Individually evaluated	140,061	180,965
Collectively evaluated	32,954	34,290
Total impaired loans	173,015	215,255
Collectively evaluated	6,397,985	6,273,759
Total loans	6,571,000	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	(83)	(512)
Recoveries	145	74
Net charge offs	62	(438)
Provision for loan losses	(5,551)	(4,208)
Balance at end of period	8,545	14,034
Allowance for loan losses:
Individually evaluated	187	0
Collectively evaluated	339	295
Total impaired loans	526	295
Collectively evaluated	8,019	13,739
Balance at end of period	8,545	14,034
Loans:
Individually evaluated	15,303	8,439
Collectively evaluated	4,642	6,595
Total impaired loans	19,945	15,034
Collectively evaluated	825,391	882,690
Total loans	845,336	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	(803)	(1,504)
Recoveries	163	1,624
Net charge offs	(640)	120
Provision for loan losses	(3,155)	2,147
Balance at end of period	41,490	45,285
Allowance for loan losses:
Individually evaluated	183	3,117
Collectively evaluated	147	424
Total impaired loans	330	3,541
Collectively evaluated	41,160	41,744
Balance at end of period	41,490	45,285
Loans:
Individually evaluated	6,799	17,322
Collectively evaluated	15,035	16,018
Total impaired loans	21,834	33,340
Collectively evaluated	3,307,751	3,541,392
Total loans	3,329,585	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	(62)	(558)
Recoveries	47	203
Net charge offs	(15)	(355)
Provision for loan losses	4,571	2,021
Balance at end of period	31,488	26,932
Allowance for loan losses:
Individually evaluated	0	0
Collectively evaluated	707	441
Total impaired loans	707	441
Collectively evaluated	30,781	26,491
Balance at end of period	31,488	26,932
Loans:
Individually evaluated	220	0
Collectively evaluated	1,818	1,203
Total impaired loans	2,038	1,203
Collectively evaluated	1,649,767	1,431,294
Total loans	1,651,805	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	(1,034)	(4,332)
Recoveries	342	755
Net charge offs	(692)	(3,577)
Provision for loan losses	5,212	2,362
Balance at end of period	31,566	27,046
Allowance for loan losses:
Individually evaluated	106	147
Collectively evaluated	10,543	10,944
Total impaired loans	10,649	11,091
Collectively evaluated	20,917	15,955
Balance at end of period	31,566	27,046
Loans:
Individually evaluated	11,060	7,033
Collectively evaluated	58,539	61,303
Total impaired loans	69,599	68,336
Collectively evaluated	7,045,858	6,263,991
Total loans	7,115,457	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	(1,196)	(4,686)
Recoveries	1,423	3,491
Net charge offs	227	(1,195)
Provision for loan losses	(351)	(1,996)
Balance at end of period	20,240	20,364
Allowance for loan losses:
Individually evaluated	0	3
Collectively evaluated	9,665	9,309
Total impaired loans	9,665	9,312
Collectively evaluated	10,575	11,052
Balance at end of period	20,240	20,364
Loans:
Individually evaluated	643	650
Collectively evaluated	20,824	20,107
Total impaired loans	21,467	20,757
Collectively evaluated	875,644	913,686
Total loans	897,111	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	(2,140)	(3,831)
Recoveries	378	820
Net charge offs	(1,762)	(3,011)
Provision for loan losses	1,979	2,034
Balance at end of period	4,765	4,548
Allowance for loan losses:
Individually evaluated	0	0
Collectively evaluated	229	186
Total impaired loans	229	186
Collectively evaluated	4,536	4,362
Balance at end of period	4,765	4,548
Loans:
Individually evaluated	0	0
Collectively evaluated	1,315	1,235
Total impaired loans	1,315	1,235
Collectively evaluated	371,460	392,744
Total loans	$ 372,775	$ 393,979