Allowance for Credit Losses - Amortized Cost Basis by Year of Origination and Credit Quality Indicator (Details) - USD ($)	Jun. 30, 2021	Dec. 31, 2020
Credit quality
2020/2021		$ 2,543,705,000
2019/2020		2,120,213,000
2018/2019		1,644,201,000
2017/2018		1,291,172,000
2016/2017		882,520,000
Prior		2,236,923,000
Revolving Loans Amortized Cost Basis		2,516,240,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		44,123,000
Total amortized cost basis		13,279,097,000
Loans and Leases	$ 13,103,785,000	13,279,097,000
Loss
Credit quality
Loans and Leases	0	0
Residential mortgage
Credit quality
2020/2021	671,281,000	864,559,000
2019/2020	803,083,000	482,495,000
2018/2019	418,810,000	389,725,000
2017/2018	308,919,000	471,962,000
2016/2017	388,376,000	391,156,000
Prior	1,230,158,000	1,089,580,000
Revolving Loans Amortized Cost Basis	625,000	578,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	155,000	163,000
Total amortized cost basis	3,821,407,000	3,690,218,000
Residential mortgage | 740 and greater
Credit quality
2020/2021	570,542,000	728,807,000
2019/2020	675,163,000	384,248,000
2018/2019	329,047,000	290,484,000
2017/2018	224,827,000	361,297,000
2016/2017	293,853,000	314,971,000
Prior	958,515,000	830,795,000
Total amortized cost basis	3,051,947,000	2,910,602,000
Residential mortgage | 680 - 739
Credit quality
2020/2021	68,225,000	85,151,000
2019/2020	86,857,000	53,090,000
2018/2019	50,699,000	44,616,000
2017/2018	43,075,000	50,703,000
2016/2017	42,753,000	39,230,000
Prior	144,223,000	144,537,000
Total amortized cost basis	435,832,000	417,327,000
Residential mortgage | 620 - 679
Credit quality
2020/2021	11,867,000	15,767,000
2019/2020	12,564,000	7,604,000
2018/2019	9,988,000	11,460,000
2017/2018	6,352,000	9,628,000
2016/2017	9,310,000	7,982,000
Prior	41,478,000	43,393,000
Total amortized cost basis	91,559,000	95,834,000
Residential mortgage | 550 - 619
Credit quality
2019/2020	1,018,000	1,971,000
2018/2019	171,000	2,818,000
2017/2018	1,322,000	2,920,000
2016/2017	1,752,000	4,474,000
Prior	11,788,000	10,144,000
Total amortized cost basis	16,051,000	22,327,000
Residential mortgage | Less than 550
Credit quality
2019/2020	1,274,000	861,000
2018/2019		593,000
2017/2018	346,000	2,916,000
2016/2017	2,545,000	594,000
Prior	2,807,000	2,138,000
Total amortized cost basis	6,972,000	7,102,000
Residential mortgage | No Score
Credit quality
2020/2021	10,207,000	13,823,000
2019/2020	8,602,000	18,861,000
2018/2019	15,988,000	21,214,000
2017/2018	21,087,000	21,821,000
2016/2017	18,814,000	14,355,000
Prior	51,217,000	45,147,000
Total amortized cost basis	125,915,000	135,221,000
Residential mortgage | Other
Credit quality
2020/2021	10,440,000	21,011,000
2019/2020	17,605,000	15,860,000
2018/2019	12,917,000	18,540,000
2017/2018	11,910,000	22,677,000
2016/2017	19,349,000	9,550,000
Prior	20,130,000	13,426,000
Revolving Loans Amortized Cost Basis	625,000	578,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	155,000	163,000
Total amortized cost basis	93,131,000	101,805,000
Home equity
Credit quality
Revolving Loans Amortized Cost Basis		833,521,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		8,103,000
Total amortized cost basis		841,624,000
Home equity | 740 and greater
Credit quality
Revolving Loans Amortized Cost Basis		608,282,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		2,163,000
Total amortized cost basis		610,445,000
Home equity | 680 - 739
Credit quality
Revolving Loans Amortized Cost Basis		159,886,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		3,155,000
Total amortized cost basis		163,041,000
Home equity | 620 - 679
Credit quality
Revolving Loans Amortized Cost Basis		44,005,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		1,571,000
Total amortized cost basis		45,576,000
Home equity | 550 - 619
Credit quality
Revolving Loans Amortized Cost Basis		11,644,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		884,000
Total amortized cost basis		12,528,000
Home equity | Less than 550
Credit quality
Revolving Loans Amortized Cost Basis		5,159,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		330,000
Total amortized cost basis		5,489,000
Home equity | No Score
Credit quality
Revolving Loans Amortized Cost Basis		4,545,000
Total amortized cost basis		4,545,000
Consumer loans
Credit quality
2020/2021		250,019,000
2019/2020		295,128,000
2018/2019		226,757,000
2017/2018		139,788,000
2016/2017		62,534,000
Prior		25,576,000
Revolving Loans Amortized Cost Basis		349,158,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		4,882,000
Total amortized cost basis		1,353,842,000
Consumer loans | 740 and greater
Credit quality
2020/2021		113,373,000
2019/2020		122,965,000
2018/2019		99,678,000
2017/2018		54,691,000
2016/2017		24,029,000
Prior		6,034,000
Revolving Loans Amortized Cost Basis		114,748,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		275,000
Total amortized cost basis		535,793,000
Consumer loans | 680 - 739
Credit quality
2020/2021		83,316,000
2019/2020		90,853,000
2018/2019		66,143,000
2017/2018		36,426,000
2016/2017		16,358,000
Prior		4,985,000
Revolving Loans Amortized Cost Basis		76,391,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		773,000
Total amortized cost basis		375,245,000
Consumer loans | 620 - 679
Credit quality
2020/2021		40,469,000
2019/2020		48,904,000
2018/2019		33,917,000
2017/2018		24,705,000
2016/2017		11,144,000
Prior		3,788,000
Revolving Loans Amortized Cost Basis		36,622,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		1,221,000
Total amortized cost basis		200,770,000
Consumer loans | 550 - 619
Credit quality
2020/2021		9,125,000
2019/2020		20,274,000
2018/2019		17,693,000
2017/2018		15,126,000
2016/2017		7,825,000
Prior		2,883,000
Revolving Loans Amortized Cost Basis		12,980,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		1,458,000
Total amortized cost basis		87,364,000
Consumer loans | Less than 550
Credit quality
2020/2021		3,017,000
2019/2020		10,139,000
2018/2019		9,189,000
2017/2018		6,517,000
2016/2017		3,123,000
Prior		1,118,000
Revolving Loans Amortized Cost Basis		5,261,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		799,000
Total amortized cost basis		39,163,000
Consumer loans | No Score
Credit quality
2020/2021		339,000
2019/2020		103,000
2018/2019		64,000
2017/2018		109,000
2016/2017		10,000
Revolving Loans Amortized Cost Basis		33,854,000
Revolving Loans Converted to Term Loans Amortized Cost Basis		356,000
Total amortized cost basis		34,835,000
Consumer loans | Other
Credit quality
2020/2021		380,000
2019/2020		1,890,000
2018/2019		73,000
2017/2018		2,214,000
2016/2017		45,000
Prior		6,768,000
Revolving Loans Amortized Cost Basis		69,302,000
Total amortized cost basis		80,672,000
Residential and consumer
Credit quality
2020/2021	1,818,668,000
2019/2020	1,992,502,000
2018/2019	1,928,978,000
2017/2018	1,424,076,000
2016/2017	1,110,131,000
Prior	2,769,127,000
Revolving Loans Amortized Cost Basis	2,021,085,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	39,218,000
Total amortized cost basis	13,103,785,000
Residential
Credit quality
2020/2021	671,281,000	864,559,000
2019/2020	803,083,000	482,495,000
2018/2019	418,810,000	389,725,000
2017/2018	308,919,000	471,962,000
2016/2017	388,376,000	391,156,000
Prior	1,230,158,000	1,089,580,000
Revolving Loans Amortized Cost Basis	817,278,000	834,099,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	8,870,000	8,266,000
Total amortized cost basis	4,646,775,000	4,531,842,000
Residential | Residential mortgage
Credit quality
Loans and Leases	3,821,407,000	3,690,218,000
Home equity Line | Home equity
Credit quality
Loans and Leases	825,368,000	841,624,000
Consumer
Credit quality
2020/2021	158,666,000
2019/2020	213,328,000
2018/2019	237,027,000
2017/2018	171,152,000
2016/2017	99,480,000
Prior	46,451,000
Revolving Loans Amortized Cost Basis	336,764,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	4,691,000
Total amortized cost basis	1,267,559,000
Consumer | 740 and greater
Credit quality
2020/2021	82,086,000
2019/2020	97,867,000
2018/2019	100,874,000
2017/2018	77,671,000
2016/2017	38,340,000
Prior	16,537,000
Revolving Loans Amortized Cost Basis	112,925,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	284,000
Total amortized cost basis	526,584,000
Consumer | 680 - 739
Credit quality
2020/2021	50,771,000
2019/2020	70,303,000
2018/2019	73,024,000
2017/2018	48,071,000
2016/2017	26,097,000
Prior	12,183,000
Revolving Loans Amortized Cost Basis	70,627,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	747,000
Total amortized cost basis	351,823,000
Consumer | 620 - 679
Credit quality
2020/2021	21,372,000
2019/2020	31,170,000
2018/2019	37,145,000
2017/2018	25,852,000
2016/2017	17,799,000
Prior	9,120,000
Revolving Loans Amortized Cost Basis	31,515,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	1,258,000
Total amortized cost basis	175,231,000
Consumer | 550 - 619
Credit quality
2020/2021	2,887,000
2019/2020	9,729,000
2018/2019	17,206,000
2017/2018	14,016,000
2016/2017	11,217,000
Prior	6,263,000
Revolving Loans Amortized Cost Basis	10,652,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	1,234,000
Total amortized cost basis	73,204,000
Consumer | Less than 550
Credit quality
2020/2021	322,000
2019/2020	3,826,000
2018/2019	6,934,000
2017/2018	5,439,000
2016/2017	3,757,000
Prior	2,295,000
Revolving Loans Amortized Cost Basis	3,184,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	748,000
Total amortized cost basis	26,505,000
Consumer | No Score
Credit quality
2020/2021	834,000
2019/2020	63,000
2018/2019	85,000
2017/2018	51,000
2016/2017	87,000
Prior	4,000
Revolving Loans Amortized Cost Basis	33,144,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	420,000
Total amortized cost basis	34,688,000
Consumer | Other
Credit quality
2020/2021	394,000
2019/2020	370,000
2018/2019	1,759,000
2017/2018	52,000
2016/2017	2,183,000
Prior	49,000
Revolving Loans Amortized Cost Basis	74,717,000
Total amortized cost basis	79,524,000
Consumer | Consumer loans
Credit quality
Loans and Leases	1,267,559,000	1,353,842,000
Home equity line
Credit quality
Revolving Loans Amortized Cost Basis	816,653,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	8,715,000
Total amortized cost basis	825,368,000
Home equity line | 740 and greater
Credit quality
Revolving Loans Amortized Cost Basis	610,924,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	1,757,000
Total amortized cost basis	612,681,000
Home equity line | 680 - 739
Credit quality
Revolving Loans Amortized Cost Basis	147,286,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	3,619,000
Total amortized cost basis	150,905,000
Home equity line | 620 - 679
Credit quality
Revolving Loans Amortized Cost Basis	39,660,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	2,036,000
Total amortized cost basis	41,696,000
Home equity line | 550 - 619
Credit quality
Revolving Loans Amortized Cost Basis	12,966,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	1,256,000
Total amortized cost basis	14,222,000
Home equity line | Less than 550
Credit quality
Revolving Loans Amortized Cost Basis	2,025,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	47,000
Total amortized cost basis	2,072,000
Home equity line | No Score
Credit quality
Revolving Loans Amortized Cost Basis	3,792,000
Total amortized cost basis	3,792,000
Commercial and Industrial
Credit quality
2020/2021	616,699,000	931,522,000
2019/2020	447,374,000	349,849,000
2018/2019	288,908,000	215,307,000
2017/2018	171,682,000	81,113,000
2016/2017	53,921,000	56,095,000
Prior	221,845,000	111,069,000
Revolving Loans Amortized Cost Basis	738,463,000	1,243,900,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	25,655,000	30,652,000
Total amortized cost basis	2,564,547,000	3,019,507,000
Loans and Leases	2,564,547,000	3,019,507,000
Commercial and Industrial | Pass
Credit quality
2020/2021	606,765,000	873,639,000
2019/2020	422,457,000	324,030,000
2018/2019	242,554,000	183,329,000
2017/2018	136,069,000	73,000,000
2016/2017	48,828,000	49,886,000
Prior	207,502,000	94,360,000
Revolving Loans Amortized Cost Basis	674,340,000	1,058,786,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	23,935,000	28,853,000
Total amortized cost basis	2,362,450,000	2,685,883,000
Commercial and Industrial | Special mention
Credit quality
2020/2021	122,000	20,937,000
2019/2020	8,994,000	10,370,000
2018/2019	33,617,000	20,164,000
2017/2018	12,735,000	2,099,000
2016/2017	1,425,000	279,000
Prior	4,647,000	8,316,000
Revolving Loans Amortized Cost Basis	14,338,000	101,183,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	376,000	1,549,000
Total amortized cost basis	76,254,000	164,897,000
Commercial and Industrial | Substandard
Credit quality
2020/2021		23,804,000
2019/2020	7,149,000	2,023,000
2018/2019	2,400,000	2,568,000
2017/2018	16,246,000	677,000
2016/2017	137,000	4,063,000
Prior	8,731,000	8,113,000
Revolving Loans Amortized Cost Basis	6,397,000	33,775,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	1,344,000	250,000
Total amortized cost basis	42,404,000	75,273,000
Commercial and Industrial | Other
Credit quality
2020/2021	9,812,000	13,142,000
2019/2020	8,774,000	13,426,000
2018/2019	10,337,000	9,246,000
2017/2018	6,632,000	5,337,000
2016/2017	3,531,000	1,867,000
Prior	965,000	280,000
Revolving Loans Amortized Cost Basis	43,388,000	50,156,000
Total amortized cost basis	83,439,000	93,454,000
Commercial Real Estate
Credit quality
2020/2021	288,366,000	344,374,000
2019/2020	343,906,000	678,824,000
2018/2019	624,460,000	586,274,000
2017/2018	580,630,000	484,627,000
2016/2017	484,642,000	343,882,000
Prior	1,134,181,000	894,258,000
Revolving Loans Amortized Cost Basis	71,881,000	60,114,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	2,000	323,000
Total amortized cost basis	3,528,068,000	3,392,676,000
Loans and Leases	3,528,068,000	3,392,676,000
Commercial Real Estate | Pass
Credit quality
2020/2021	288,366,000	342,845,000
2019/2020	342,013,000	611,243,000
2018/2019	571,608,000	541,104,000
2017/2018	557,533,000	447,366,000
2016/2017	449,551,000	295,426,000
Prior	1,055,803,000	814,398,000
Revolving Loans Amortized Cost Basis	63,775,000	47,604,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	2,000	323,000
Total amortized cost basis	3,328,651,000	3,100,309,000
Commercial Real Estate | Special mention
Credit quality
2020/2021		1,500,000
2019/2020	1,482,000	63,617,000
2018/2019	52,852,000	26,187,000
2017/2018	16,081,000	33,482,000
2016/2017	33,022,000	37,841,000
Prior	55,933,000	61,279,000
Revolving Loans Amortized Cost Basis	7,604,000	2,999,000
Total amortized cost basis	166,974,000	226,905,000
Commercial Real Estate | Substandard
Credit quality
2020/2021		29,000
2019/2020	411,000	3,964,000
2018/2019		18,983,000
2017/2018	7,016,000	3,779,000
2016/2017	2,069,000	10,615,000
Prior	21,962,000	18,083,000
Revolving Loans Amortized Cost Basis	502,000	9,511,000
Total amortized cost basis	31,960,000	64,964,000
Commercial Real Estate | Other
Credit quality
Prior	483,000	498,000
Total amortized cost basis	483,000	498,000
Construction
Credit quality
2020/2021	61,421,000	70,509,000
2019/2020	112,185,000	250,631,000
2018/2019	302,146,000	211,831,000
2017/2018	179,811,000	94,034,000
2016/2017	65,936,000	25,492,000
Prior	75,667,000	54,353,000
Revolving Loans Amortized Cost Basis	56,699,000	28,969,000
Total amortized cost basis	853,865,000	735,819,000
Loans and Leases	853,865,000	735,819,000
Construction | Pass
Credit quality
2020/2021	49,592,000	53,931,000
2019/2020	97,149,000	233,730,000
2018/2019	296,405,000	202,808,000
2017/2018	173,352,000	83,792,000
2016/2017	62,983,000	23,171,000
Prior	70,998,000	41,536,000
Revolving Loans Amortized Cost Basis	55,892,000	28,386,000
Total amortized cost basis	806,371,000	667,354,000
Construction | Special mention
Credit quality
2019/2020		508,000
2018/2019	494,000	707,000
2017/2018	705,000	4,717,000
Prior	361,000	9,172,000
Total amortized cost basis	1,560,000	15,104,000
Construction | Substandard
Credit quality
2018/2019		541,000
2017/2018	373,000	1,840,000
2016/2017		521,000
Prior	1,378,000	989,000
Total amortized cost basis	1,751,000	3,891,000
Construction | Other
Credit quality
2020/2021	11,829,000	16,578,000
2019/2020	15,036,000	16,393,000
2018/2019	5,247,000	7,775,000
2017/2018	5,381,000	3,685,000
2016/2017	2,953,000	1,800,000
Prior	2,930,000	2,656,000
Revolving Loans Amortized Cost Basis	807,000	583,000
Total amortized cost basis	44,183,000	49,470,000
Lease financing
Credit quality
2020/2021	22,235,000	82,722,000
2019/2020	72,626,000	63,286,000
2018/2019	57,627,000	14,307,000
2017/2018	11,882,000	19,648,000
2016/2017	17,776,000	3,361,000
Prior	60,825,000	62,087,000
Total amortized cost basis	242,971,000	245,411,000
Loans and Leases	242,971,000	245,411,000
Lease financing | Pass
Credit quality
2020/2021	21,690,000	79,064,000
2019/2020	69,598,000	60,717,000
2018/2019	55,494,000	13,669,000
2017/2018	11,376,000	17,207,000
2016/2017	16,623,000	3,010,000
Prior	60,091,000	61,266,000
Total amortized cost basis	234,872,000	234,933,000
Lease financing | Special mention
Credit quality
2020/2021	545,000	950,000
2019/2020	308,000	892,000
2018/2019	465,000	311,000
2017/2018	246,000	1,300,000
2016/2017	81,000	351,000
Prior	232,000	295,000
Total amortized cost basis	1,877,000	4,099,000
Lease financing | Substandard
Credit quality
2020/2021		2,708,000
2019/2020	2,720,000	1,677,000
2018/2019	1,668,000	327,000
2017/2018	260,000	1,141,000
2016/2017	1,072,000
Prior	502,000	526,000
Total amortized cost basis	6,222,000	6,379,000
Commercial Lending
Credit quality
2020/2021	988,721,000	1,429,127,000
2019/2020	976,091,000	1,342,590,000
2018/2019	1,273,141,000	1,027,719,000
2017/2018	944,005,000	679,422,000
2016/2017	622,275,000	428,830,000
Prior	1,492,518,000	1,121,767,000
Revolving Loans Amortized Cost Basis	867,043,000	1,332,983,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	25,657,000	30,975,000
Total amortized cost basis	$ 7,189,451,000	$ 7,393,413,000