Loans, Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 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	(45,866)	(52,280)
Recoveries	8,382	22,242
Net charge offs	(37,484)	(30,038)
Provision for loan losses	31,000	38,000
Balance at end of period	267,780	274,264
Allowance for loan losses:
Individually evaluated for impairment	224	7,963
Collectively evaluated for impairment	267,556	266,301
Balance at end of period	267,780	274,264
Loans [Abstract]
Individually evaluated for impairment	217,028	111,487
Collectively evaluated for impairment	19,598,258	18,602,856
Total loans	19,815,286	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	(37,522)	(27,687)
Recoveries	4,022	9,821
Net charge offs	(33,500)	(17,866)
Provision for loan losses	38,128	30,190
Balance at end of period	134,587	129,959
Allowance for loan losses:
Individually evaluated for impairment	0	7,522
Collectively evaluated for impairment	134,587	122,437
Balance at end of period	134,587	129,959
Loans [Abstract]
Individually evaluated for impairment	191,752	91,569
Collectively evaluated for impairment	6,510,234	6,099,114
Total loans	6,701,986	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	(106)	(2,645)
Recoveries	43	921
Net charge offs	(63)	(1,724)
Provision for loan losses	(2,767)	3,894
Balance at end of period	15,850	18,680
Allowance for loan losses:
Individually evaluated for impairment	165	0
Collectively evaluated for impairment	15,685	18,680
Balance at end of period	15,850	18,680
Loans [Abstract]
Individually evaluated for impairment	7,790	6,221
Collectively evaluated for impairment	913,946	911,991
Total loans	921,736	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	(887)	(4,645)
Recoveries	1,566	4,157
Net charge offs	679	(488)
Provision for loan losses	(2,666)	(2,827)
Balance at end of period	41,031	43,018
Allowance for loan losses:
Individually evaluated for impairment	45	229
Collectively evaluated for impairment	40,986	42,789
Balance at end of period	41,031	43,018
Loans [Abstract]
Individually evaluated for impairment	10,036	5,460
Collectively evaluated for impairment	3,485,755	3,228,806
Total loans	3,495,791	3,234,266
Real Estate Construction Portfolio Segment [Member]
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	25,266	20,999
Charge offs	(330)	(750)
Recoveries	83	2,268
Net charge offs	(247)	1,518
Provision for loan losses	(3,679)	2,749
Balance at end of period	21,340	25,266
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	21,340	25,266
Balance at end of period	21,340	25,266
Loans [Abstract]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	1,285,573	1,162,145
Total loans	1,285,573	1,162,145
Residential Portfolio Segment [Member]
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	28,261	31,926
Charge offs	(2,334)	(5,636)
Recoveries	345	1,077
Net charge offs	(1,989)	(4,559)
Provision for loan losses	1,624	894
Balance at end of period	27,896	28,261
Allowance for loan losses:
Individually evaluated for impairment	14	166
Collectively evaluated for impairment	27,882	28,095
Balance at end of period	27,896	28,261
Loans [Abstract]
Individually evaluated for impairment	6,800	6,956
Collectively evaluated for impairment	6,028,920	5,776,311
Total loans	6,035,720	5,783,267
Home Equity Portfolio Segments [Member]
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	23,555	26,464
Charge offs	(2,702)	(7,048)
Recoveries	1,873	3,233
Net charge offs	(829)	(3,815)
Provision for loan losses	(1,224)	906
Balance at end of period	21,502	23,555
Allowance for loan losses:
Individually evaluated for impairment	0	46
Collectively evaluated for impairment	21,502	23,509
Balance at end of period	21,502	23,555
Loans [Abstract]
Individually evaluated for impairment	650	1,281
Collectively evaluated for impairment	968,121	1,004,521
Total loans	968,771	1,005,802
Other consumer [Member]
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	5,525	6,435
Charge offs	(1,985)	(3,869)
Recoveries	450	765
Net charge offs	(1,535)	(3,104)
Provision for loan losses	1,584	2,194
Balance at end of period	5,574	5,525
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	5,574	5,525
Balance at end of period	5,574	5,525
Loans [Abstract]
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	405,709	419,968
Total loans	$ 405,709	$ 419,968