Loans, Changes in the Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2019	Dec. 31, 2018
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	$ 238,023	$ 265,880
Charge offs	(57,560)	(50,536)
Recoveries	16,462	20,179
Net Charge offs	(41,098)	(30,358)
Provision for loan losses	17,500	2,500
Balance at end of period	214,425	238,023
Allowance for loan losses
Individually evaluated			$ 23,291	$ 15,304
Collectively evaluated			191,133	222,719
Total allowance for loan losses	214,425	265,880	214,425	238,023
Loans
Individually evaluated			119,925	133,690
Collectively evaluated			22,633,075	22,801,887
Acquired and accounted for under ASC 310-30(a)			1,710	4,853
Total loans			22,754,710	22,940,429
Commercial and industrial
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	108,835	123,068
Charge offs	(49,845)	(30,837)
Recoveries	10,322	13,714
Net Charge offs	(39,523)	(17,123)
Provision for loan losses	36,419	2,890
Balance at end of period	105,730	108,835
Allowance for loan losses
Individually evaluated			17,791	5,721
Collectively evaluated			87,939	103,114
Total allowance for loan losses	108,835	108,835	105,730	108,835
Loans
Individually evaluated			70,568	63,153
Collectively evaluated			7,424,690	7,331,898
Acquired and accounted for under ASC 310-30(a)			365	2,994
Total loans			7,495,623	7,398,044
Commercial real estate — owner occupied
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	9,255	10,352
Charge offs	(222)	(1,363)
Recoveries	2,795	639
Net Charge offs	2,573	(724)
Provision for loan losses	(3,229)	(373)
Balance at end of period	8,599	9,255
Allowance for loan losses
Individually evaluated			19	24
Collectively evaluated			8,579	9,231
Total allowance for loan losses	8,599	10,352	8,599	9,255
Loans
Individually evaluated			1,912	5,852
Collectively evaluated			912,935	913,708
Acquired and accounted for under ASC 310-30(a)			677	883
Total loans			915,524	920,443
Commercial real estate — investor
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	40,844	41,059
Charge offs	0	(7,914)
Recoveries	31	668
Net Charge offs	31	(7,246)
Provision for loan losses	(971)	7,031
Balance at end of period	39,904	40,844
Allowance for loan losses
Individually evaluated			101	28
Collectively evaluated			39,803	40,816
Total allowance for loan losses	40,844	40,844	39,904	40,844
Loans
Individually evaluated			5,104	2,384
Collectively evaluated			3,798,039	3,748,883
Acquired and accounted for under ASC 310-30(a)			134	287
Total loans			3,803,277	3,751,554
Real estate construction
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	28,240	34,370
Charge offs	(60)	(298)
Recoveries	230	446
Net Charge offs	170	149
Provision for loan losses	(4,960)	(6,279)
Balance at end of period	23,451	28,240
Allowance for loan losses
Individually evaluated			56	75
Collectively evaluated			23,395	28,165
Total allowance for loan losses	28,240	28,240	23,451	28,240
Loans
Individually evaluated			409	510
Collectively evaluated			1,356,088	1,334,500
Acquired and accounted for under ASC 310-30(a)			11	21
Total loans			1,356,508	1,335,031
Residential mortgage
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	25,595	29,607
Charge offs	(1,754)	(1,627)
Recoveries	539	1,271
Net Charge offs	(1,215)	(355)
Provision for loan losses	(5,757)	(3,657)
Balance at end of period	18,623	25,595
Allowance for loan losses
Individually evaluated			3,824	6,023
Collectively evaluated			14,799	19,572
Total allowance for loan losses	18,623	29,607	18,623	25,595
Loans
Individually evaluated			36,039	50,486
Collectively evaluated			7,918,265	8,226,642
Acquired and accounted for under ASC 310-30(a)			497	584
Total loans			7,954,801	8,277,712
Home equity
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	19,266	22,126
Charge offs	(1,605)	(3,236)
Recoveries	1,878	2,628
Net Charge offs	273	(608)
Provision for loan losses	(7,690)	(2,252)
Balance at end of period	11,849	19,266
Allowance for loan losses
Individually evaluated			1,313	3,312
Collectively evaluated			10,536	15,954
Total allowance for loan losses	19,266	19,266	11,849	19,266
Loans
Individually evaluated			4,648	10,124
Collectively evaluated			874,968	884,266
Acquired and accounted for under ASC 310-30(a)			26	83
Total loans			879,642	894,473
Other consumer
Changes in the allowance for loan losses by portfolio segment
Balance at beginning of period	5,988	5,298
Charge offs	(4,074)	(5,261)
Recoveries	667	812
Net Charge offs	(3,407)	(4,448)
Provision for loan losses	3,688	5,138
Balance at end of period	6,269	5,988
Allowance for loan losses
Individually evaluated			187	121
Collectively evaluated			6,082	5,867
Total allowance for loan losses	$ 6,269	$ 5,298	6,269	5,988
Loans
Individually evaluated			1,244	1,181
Collectively evaluated			348,091	361,990
Acquired and accounted for under ASC 310-30(a)			0	0
Total loans			$ 349,335	$ 363,171