Loans, Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	$ 238,023	$ 265,880
Charge offs	(74,313)	(50,536)
Recoveries	19,161	20,179
Net charge offs	(55,152)	(30,358)
Provision for loan losses	18,500	2,500
Balance at end of period	201,371	238,023
Allowance for loan losses:
Individually evaluated for impairment	16,165	15,304
Collectively evaluated for impairment	185,205	222,719
Balance at end of period	201,371	238,023
Loans:
Individually evaluated for impairment	110,043	133,690
Collectively evaluated for impairment	22,709,845	22,801,887
Acquired and accounted for under ASC 310-30(a)	1,552	4,853
Loans and Leases Receivable, Net of Deferred Income	22,821,440	22,940,429
Commercial and industrial
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	108,835	123,068
Charge offs	(63,315)	(30,837)
Recoveries	11,875	13,714
Net charge offs	(51,441)	(17,123)
Provision for loan losses	33,738	2,890
Balance at end of period	91,133	108,835
Allowance for loan losses:
Individually evaluated for impairment	12,010	5,721
Collectively evaluated for impairment	79,123	103,114
Balance at end of period	91,133	108,835
Loans:
Individually evaluated for impairment	62,035	63,153
Collectively evaluated for impairment	7,292,217	7,331,898
Acquired and accounted for under ASC 310-30(a)	342	2,994
Loans and Leases Receivable, Net of Deferred Income	7,354,594	7,398,044
Commercial real estate - owner occupied
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	9,255	10,352
Charge offs	(222)	(1,363)
Recoveries	2,795	639
Net charge offs	2,573	(724)
Provision for loan losses	(1,543)	(373)
Balance at end of period	10,284	9,255
Allowance for loan losses:
Individually evaluated for impairment	19	24
Collectively evaluated for impairment	10,265	9,231
Balance at end of period	10,284	9,255
Loans:
Individually evaluated for impairment	1,676	5,852
Collectively evaluated for impairment	909,010	913,708
Acquired and accounted for under ASC 310-30(a)	579	883
Loans and Leases Receivable, Net of Deferred Income	911,265	920,443
Commercial real estate - investor
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	40,844	41,059
Charge offs	0	(7,914)
Recoveries	31	668
Net charge offs	31	(7,246)
Provision for loan losses	(361)	7,031
Balance at end of period	40,514	40,844
Allowance for loan losses:
Individually evaluated for impairment	15	28
Collectively evaluated for impairment	40,498	40,816
Balance at end of period	40,514	40,844
Loans:
Individually evaluated for impairment	4,633	2,384
Collectively evaluated for impairment	3,789,755	3,748,883
Acquired and accounted for under ASC 310-30(a)	129	287
Loans and Leases Receivable, Net of Deferred Income	3,794,517	3,751,554
Real estate construction
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	28,240	34,370
Charge offs	(60)	(298)
Recoveries	302	446
Net charge offs	243	149
Provision for loan losses	(3,568)	(6,279)
Balance at end of period	24,915	28,240
Allowance for loan losses:
Individually evaluated for impairment	67	75
Collectively evaluated for impairment	24,848	28,165
Balance at end of period	24,915	28,240
Loans:
Individually evaluated for impairment	477	510
Collectively evaluated for impairment	1,420,416	1,334,500
Acquired and accounted for under ASC 310-30(a)	7	21
Loans and Leases Receivable, Net of Deferred Income	1,420,900	1,335,031
Residential mortgage
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	25,595	29,607
Charge offs	(3,322)	(1,627)
Recoveries	692	1,271
Net charge offs	(2,630)	(355)
Provision for loan losses	(6,005)	(3,657)
Balance at end of period	16,960	25,595
Allowance for loan losses:
Individually evaluated for impairment	2,740	6,023
Collectively evaluated for impairment	14,220	19,572
Balance at end of period	16,960	25,595
Loans:
Individually evaluated for impairment	35,554	50,486
Collectively evaluated for impairment	8,100,958	8,226,642
Acquired and accounted for under ASC 310-30(a)	469	584
Loans and Leases Receivable, Net of Deferred Income	8,136,980	8,277,712
Home equity
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	19,266	22,126
Charge offs	(1,846)	(3,236)
Recoveries	2,599	2,628
Net charge offs	753	(608)
Provision for loan losses	(9,093)	(2,252)
Balance at end of period	10,926	19,266
Allowance for loan losses:
Individually evaluated for impairment	1,190	3,312
Collectively evaluated for impairment	9,737	15,954
Balance at end of period	10,926	19,266
Loans:
Individually evaluated for impairment	4,422	10,124
Collectively evaluated for impairment	847,577	884,266
Acquired and accounted for under ASC 310-30(a)	26	83
Loans and Leases Receivable, Net of Deferred Income	852,025	894,473
Other consumer
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of year	5,988	5,298
Charge offs	(5,548)	(5,261)
Recoveries	868	812
Net charge offs	(4,681)	(4,448)
Provision for loan losses	5,332	5,138
Balance at end of period	6,639	5,988
Allowance for loan losses:
Individually evaluated for impairment	125	121
Collectively evaluated for impairment	6,514	5,867
Balance at end of period	6,639	5,988
Loans:
Individually evaluated for impairment	1,247	1,181
Collectively evaluated for impairment	349,912	361,990
Acquired and accounted for under ASC 310-30(a)	0	0
Loans and Leases Receivable, Net of Deferred Income	$ 351,159	$ 363,171