Loans, Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	$ 274,264	$ 266,302
Charge offs	(86,439)	(52,280)
Recoveries	21,510	22,242
Net charge offs	(64,929)	(30,038)
Provision for loan losses	69,000	38,000
Balance at end of period	278,335	274,264
Allowance for loan losses:
Individually evaluated for impairment	24,103	7,963
Collectively evaluated for impairment	254,232	266,301
Balance at end of period	278,335	274,264
Loans:
Individually evaluated for impairment	214,409	111,487
Collectively evaluated for impairment	19,840,307	18,602,856
Total loans	20,054,716	18,714,343
Commercial and industrial
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	129,959	117,635
Charge offs	(71,016)	(27,687)
Recoveries	14,543	9,821
Net charge offs	(56,473)	(17,866)
Provision for loan losses	66,640	30,190
Balance at end of period	140,126	129,959
Allowance for loan losses:
Individually evaluated for impairment	20,836	7,522
Collectively evaluated for impairment	119,290	122,437
Balance at end of period	140,126	129,959
Loans:
Individually evaluated for impairment	180,965	91,569
Collectively evaluated for impairment	6,308,049	6,099,114
Total loans	6,489,014	6,190,683
Commercial real estate — owner occupied
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	18,680	16,510
Charge offs	(512)	(2,645)
Recoveries	74	921
Net charge offs	(438)	(1,724)
Provision for loan losses	4,208	3,894
Balance at end of period	14,034	18,680
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	14,034	18,680
Balance at end of period	14,034	18,680
Loans:
Individually evaluated for impairment	8,439	6,221
Collectively evaluated for impairment	889,285	911,991
Total loans	897,724	918,212
Commercial real estate — investor
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	43,018	46,333
Charge offs	(1,504)	(4,645)
Recoveries	1,624	4,157
Net charge offs	120	(488)
Provision for loan losses	2,147	2,827
Balance at end of period	45,285	43,018
Allowance for loan losses:
Individually evaluated for impairment	3,117	229
Collectively evaluated for impairment	42,168	42,789
Balance at end of period	45,285	43,018
Loans:
Individually evaluated for impairment	17,322	5,460
Collectively evaluated for impairment	3,557,410	3,228,806
Total loans	3,574,732	3,234,266
Real estate construction
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	25,266	20,999
Charge offs	(558)	(750)
Recoveries	203	2,268
Net charge offs	(355)	1,518
Provision for loan losses	2,021	2,749
Balance at end of period	26,932	25,266
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	26,932	25,266
Balance at end of period	26,932	25,266
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	1,432,497	1,162,145
Total loans	1,432,497	1,162,145
Residential mortgage
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	28,261	31,926
Charge offs	(4,332)	(5,636)
Recoveries	755	1,077
Net charge offs	(3,577)	(4,559)
Provision for loan losses	2,362	894
Balance at end of period	27,046	28,261
Allowance for loan losses:
Individually evaluated for impairment	147	166
Collectively evaluated for impairment	26,899	28,095
Balance at end of period	27,046	28,261
Loans:
Individually evaluated for impairment	7,033	6,956
Collectively evaluated for impairment	6,325,294	5,776,311
Total loans	6,332,327	5,783,267
Home equity
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	23,555	26,464
Charge offs	(4,686)	(7,048)
Recoveries	3,491	3,233
Net charge offs	(1,195)	(3,815)
Provision for loan losses	1,996	906
Balance at end of period	20,364	23,555
Allowance for loan losses:
Individually evaluated for impairment	3	46
Collectively evaluated for impairment	20,361	23,509
Balance at end of period	20,364	23,555
Loans:
Individually evaluated for impairment	650	1,281
Collectively evaluated for impairment	933,793	1,004,521
Total loans	934,443	1,005,802
Other consumer
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	5,525	6,435
Charge offs	(3,831)	(3,869)
Recoveries	820	765
Net charge offs	(3,011)	(3,104)
Provision for loan losses	2,034	2,194
Balance at end of period	4,548	5,525
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	4,548	5,525
Balance at end of period	4,548	5,525
Loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	393,979	419,968
Total loans	$ 393,979	$ 419,968