Allowance for Credit Losses - Amortized Cost Basis by Year of Origination and Credit Quality Indicator (Details) - USD ($)	Mar. 31, 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
Total Loans and Leases	$ 13,300,289,000	13,279,097,000
Loss
Credit quality
Total Loans and Leases	0	0
Residential mortgage
Credit quality
2020/2021	316,858,000	864,559,000
2019/2020	829,791,000	482,495,000
2018/2019	448,613,000	389,725,000
2017/2018	352,645,000	471,962,000
2016/2017	424,171,000	391,156,000
Prior	1,342,856,000	1,089,580,000
Revolving Loans Amortized Cost Basis	580,000	578,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	162,000	163,000
Total amortized cost basis	3,715,676,000	3,690,218,000
Residential mortgage | 740 and greater
Credit quality
2020/2021	269,847,000	728,807,000
2019/2020	698,143,000	384,248,000
2018/2019	355,459,000	290,484,000
2017/2018	261,304,000	361,297,000
2016/2017	320,423,000	314,971,000
Prior	1,031,922,000	830,795,000
Total amortized cost basis	2,937,098,000	2,910,602,000
Residential mortgage | 680 - 739
Credit quality
2020/2021	32,425,000	85,151,000
2019/2020	83,210,000	53,090,000
2018/2019	51,384,000	44,616,000
2017/2018	41,764,000	50,703,000
2016/2017	48,039,000	39,230,000
Prior	168,279,000	144,537,000
Total amortized cost basis	425,101,000	417,327,000
Residential mortgage | 620 - 679
Credit quality
2020/2021	4,220,000	15,767,000
2019/2020	15,727,000	7,604,000
2018/2019	7,626,000	11,460,000
2017/2018	11,214,000	9,628,000
2016/2017	9,310,000	7,982,000
Prior	49,018,000	43,393,000
Total amortized cost basis	97,115,000	95,834,000
Residential mortgage | 550 - 619
Credit quality
2019/2020		1,971,000
2018/2019	1,945,000	2,818,000
2017/2018	2,810,000	2,920,000
2016/2017	2,906,000	4,474,000
Prior	14,044,000	10,144,000
Total amortized cost basis	21,705,000	22,327,000
Residential mortgage | Less than 550
Credit quality
2019/2020		861,000
2018/2019	854,000	593,000
2017/2018	602,000	2,916,000
2016/2017	2,914,000	594,000
Prior	2,673,000	2,138,000
Total amortized cost basis	7,043,000	7,102,000
Residential mortgage | No Score
Credit quality
2020/2021	4,599,000	13,823,000
2019/2020	12,498,000	18,861,000
2018/2019	17,761,000	21,214,000
2017/2018	21,197,000	21,821,000
2016/2017	19,972,000	14,355,000
Prior	55,404,000	45,147,000
Total amortized cost basis	131,431,000	135,221,000
Residential mortgage | Other
Credit quality
2020/2021	5,767,000	21,011,000
2019/2020	20,213,000	15,860,000
2018/2019	13,584,000	18,540,000
2017/2018	13,754,000	22,677,000
2016/2017	20,607,000	9,550,000
Prior	21,516,000	13,426,000
Revolving Loans Amortized Cost Basis	580,000	578,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	162,000	163,000
Total amortized cost basis	96,183,000	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	966,378,000
2019/2020	2,412,170,000
2018/2019	2,059,534,000
2017/2018	1,517,679,000
2016/2017	1,177,821,000
Prior	2,985,754,000
Revolving Loans Amortized Cost Basis	2,137,285,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	43,668,000
Total amortized cost basis	13,300,289,000
Residential
Credit quality
2020/2021	316,858,000	864,559,000
2019/2020	829,791,000	482,495,000
2018/2019	448,613,000	389,725,000
2017/2018	352,645,000	471,962,000
2016/2017	424,171,000	391,156,000
Prior	1,342,856,000	1,089,580,000
Revolving Loans Amortized Cost Basis	797,471,000	834,099,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	9,017,000	8,266,000
Total amortized cost basis	4,521,422,000	4,531,842,000
Residential | Residential mortgage
Credit quality
Total Loans and Leases	3,715,676,000	3,690,218,000
Home equity Line | Home equity
Credit quality
Total Loans and Leases	805,746,000	841,624,000
Consumer
Credit quality
2020/2021	63,748,000
2019/2020	234,853,000
2018/2019	265,636,000
2017/2018	197,986,000
2016/2017	118,703,000
Prior	68,820,000
Revolving Loans Amortized Cost Basis	329,286,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	4,747,000
Total amortized cost basis	1,283,779,000
Consumer | 740 and greater
Credit quality
2020/2021	37,038,000
2019/2020	105,809,000
2018/2019	109,925,000
2017/2018	86,146,000
2016/2017	44,909,000
Prior	22,098,000
Revolving Loans Amortized Cost Basis	107,725,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	266,000
Total amortized cost basis	513,916,000
Consumer | 680 - 739
Credit quality
2020/2021	19,163,000
2019/2020	79,376,000
2018/2019	82,058,000
2017/2018	58,077,000
2016/2017	31,081,000
Prior	16,370,000
Revolving Loans Amortized Cost Basis	72,053,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	774,000
Total amortized cost basis	358,952,000
Consumer | 620 - 679
Credit quality
2020/2021	6,167,000
2019/2020	38,079,000
2018/2019	44,459,000
2017/2018	30,055,000
2016/2017	21,453,000
Prior	11,715,000
Revolving Loans Amortized Cost Basis	33,935,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	1,213,000
Total amortized cost basis	187,076,000
Consumer | 550 - 619
Credit quality
2020/2021	337,000
2019/2020	8,215,000
2018/2019	18,414,000
2017/2018	15,800,000
2016/2017	13,267,000
Prior	8,437,000
Revolving Loans Amortized Cost Basis	11,582,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	1,364,000
Total amortized cost basis	77,416,000
Consumer | Less than 550
Credit quality
2020/2021	88,000
2019/2020	2,644,000
2018/2019	8,907,000
2017/2018	7,785,000
2016/2017	5,711,000
Prior	3,445,000
Revolving Loans Amortized Cost Basis	4,181,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	719,000
Total amortized cost basis	33,480,000
Consumer | No Score
Credit quality
2020/2021	955,000
2019/2020	354,000
2018/2019	99,000
2017/2018	57,000
2016/2017	99,000
Prior	7,000
Revolving Loans Amortized Cost Basis	32,161,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	411,000
Total amortized cost basis	34,143,000
Consumer | Other
Credit quality
2019/2020	376,000
2018/2019	1,774,000
2017/2018	66,000
2016/2017	2,183,000
Prior	6,748,000
Revolving Loans Amortized Cost Basis	67,649,000
Total amortized cost basis	78,796,000
Consumer | Consumer loans
Credit quality
Total Loans and Leases	1,283,779,000	1,353,842,000
Home equity line
Credit quality
Revolving Loans Amortized Cost Basis	796,891,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	8,855,000
Total amortized cost basis	805,746,000
Home equity line | 740 and greater
Credit quality
Revolving Loans Amortized Cost Basis	589,662,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	2,108,000
Total amortized cost basis	591,770,000
Home equity line | 680 - 739
Credit quality
Revolving Loans Amortized Cost Basis	149,384,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	3,537,000
Total amortized cost basis	152,921,000
Home equity line | 620 - 679
Credit quality
Revolving Loans Amortized Cost Basis	37,325,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	1,432,000
Total amortized cost basis	38,757,000
Home equity line | 550 - 619
Credit quality
Revolving Loans Amortized Cost Basis	12,870,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	1,419,000
Total amortized cost basis	14,289,000
Home equity line | Less than 550
Credit quality
Revolving Loans Amortized Cost Basis	3,641,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	359,000
Total amortized cost basis	4,000,000
Home equity line | No Score
Credit quality
Revolving Loans Amortized Cost Basis	4,009,000
Total amortized cost basis	4,009,000
Commercial and Industrial
Credit quality
2020/2021	499,150,000	931,522,000
2019/2020	832,468,000	349,849,000
2018/2019	340,748,000	215,307,000
2017/2018	196,843,000	81,113,000
2016/2017	58,012,000	56,095,000
Prior	237,698,000	111,069,000
Revolving Loans Amortized Cost Basis	926,621,000	1,243,900,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	29,896,000	30,652,000
Total amortized cost basis	3,121,436,000	3,019,507,000
Total Loans and Leases	3,121,436,000	3,019,507,000
Commercial and Industrial | Pass
Credit quality
2020/2021	495,898,000	873,639,000
2019/2020	781,914,000	324,030,000
2018/2019	315,190,000	183,329,000
2017/2018	152,290,000	73,000,000
2016/2017	51,136,000	49,886,000
Prior	218,781,000	94,360,000
Revolving Loans Amortized Cost Basis	785,046,000	1,058,786,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	27,922,000	28,853,000
Total amortized cost basis	2,828,177,000	2,685,883,000
Commercial and Industrial | Special mention
Credit quality
2020/2021		20,937,000
2019/2020	17,608,000	10,370,000
2018/2019	10,957,000	20,164,000
2017/2018	19,751,000	2,099,000
2016/2017	1,930,000	279,000
Prior	5,373,000	8,316,000
Revolving Loans Amortized Cost Basis	66,867,000	101,183,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	607,000	1,549,000
Total amortized cost basis	123,093,000	164,897,000
Commercial and Industrial | Substandard
Credit quality
2020/2021		23,804,000
2019/2020	23,098,000	2,023,000
2018/2019	2,808,000	2,568,000
2017/2018	16,913,000	677,000
2016/2017	584,000	4,063,000
Prior	12,048,000	8,113,000
Revolving Loans Amortized Cost Basis	28,361,000	33,775,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	1,367,000	250,000
Total amortized cost basis	85,179,000	75,273,000
Commercial and Industrial | Other
Credit quality
2020/2021	3,252,000	13,142,000
2019/2020	9,848,000	13,426,000
2018/2019	11,793,000	9,246,000
2017/2018	7,889,000	5,337,000
2016/2017	4,362,000	1,867,000
Prior	1,496,000	280,000
Revolving Loans Amortized Cost Basis	46,347,000	50,156,000
Total amortized cost basis	84,987,000	93,454,000
Commercial real estate
Credit quality
2020/2021	41,958,000	344,374,000
2019/2020	348,282,000	678,824,000
2018/2019	672,693,000	586,274,000
2017/2018	586,223,000	484,627,000
2016/2017	491,574,000	343,882,000
Prior	1,196,211,000	894,258,000
Revolving Loans Amortized Cost Basis	59,284,000	60,114,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	8,000	323,000
Total amortized cost basis	3,396,233,000	3,392,676,000
Total Loans and Leases	3,396,233,000	3,392,676,000
Commercial real estate | Pass
Credit quality
2020/2021	41,958,000	342,845,000
2019/2020	346,445,000	611,243,000
2018/2019	613,930,000	541,104,000
2017/2018	556,954,000	447,366,000
2016/2017	454,433,000	295,426,000
Prior	1,104,669,000	814,398,000
Revolving Loans Amortized Cost Basis	51,280,000	47,604,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	8,000	323,000
Total amortized cost basis	3,169,677,000	3,100,309,000
Commercial real estate | Special mention
Credit quality
2020/2021		1,500,000
2019/2020	1,491,000	63,617,000
2018/2019	58,763,000	26,187,000
2017/2018	14,518,000	33,482,000
2016/2017	33,401,000	37,841,000
Prior	64,971,000	61,279,000
Revolving Loans Amortized Cost Basis		2,999,000
Total amortized cost basis	173,144,000	226,905,000
Commercial real estate | Substandard
Credit quality
2020/2021		29,000
2019/2020	346,000	3,964,000
2018/2019		18,983,000
2017/2018	14,751,000	3,779,000
2016/2017	3,740,000	10,615,000
Prior	26,082,000	18,083,000
Revolving Loans Amortized Cost Basis	8,004,000	9,511,000
Total amortized cost basis	52,923,000	64,964,000
Commercial real estate | Other
Credit quality
Prior	489,000	498,000
Total amortized cost basis	489,000	498,000
Construction
Credit quality
2020/2021	37,611,000	70,509,000
2019/2020	90,267,000	250,631,000
2018/2019	270,953,000	211,831,000
2017/2018	170,882,000	94,034,000
2016/2017	66,621,000	25,492,000
Prior	78,314,000	54,353,000
Revolving Loans Amortized Cost Basis	24,623,000	28,969,000
Total amortized cost basis	739,271,000	735,819,000
Total Loans and Leases	739,271,000	735,819,000
Construction | Pass
Credit quality
2020/2021	32,201,000	53,931,000
2019/2020	73,512,000	233,730,000
2018/2019	260,522,000	202,808,000
2017/2018	162,052,000	83,792,000
2016/2017	58,537,000	23,171,000
Prior	63,624,000	41,536,000
Revolving Loans Amortized Cost Basis	24,043,000	28,386,000
Total amortized cost basis	674,491,000	667,354,000
Construction | Special mention
Credit quality
2019/2020		508,000
2018/2019	507,000	707,000
2017/2018	706,000	4,717,000
2016/2017	4,429,000
Prior	9,172,000	9,172,000
Total amortized cost basis	14,814,000	15,104,000
Construction | Substandard
Credit quality
2018/2019		541,000
2017/2018	536,000	1,840,000
2016/2017		521,000
Prior	1,478,000	989,000
Total amortized cost basis	2,014,000	3,891,000
Construction | Other
Credit quality
2020/2021	5,410,000	16,578,000
2019/2020	16,755,000	16,393,000
2018/2019	9,924,000	7,775,000
2017/2018	7,588,000	3,685,000
2016/2017	3,655,000	1,800,000
Prior	4,040,000	2,656,000
Revolving Loans Amortized Cost Basis	580,000	583,000
Total amortized cost basis	47,952,000	49,470,000
Lease financing
Credit quality
2020/2021	7,053,000	82,722,000
2019/2020	76,509,000	63,286,000
2018/2019	60,891,000	14,307,000
2017/2018	13,100,000	19,648,000
2016/2017	18,740,000	3,361,000
Prior	61,855,000	62,087,000
Total amortized cost basis	238,148,000	245,411,000
Total Loans and Leases	238,148,000	245,411,000
Lease financing | Pass
Credit quality
2020/2021	6,487,000	79,064,000
2019/2020	73,461,000	60,717,000
2018/2019	58,375,000	13,669,000
2017/2018	12,521,000	17,207,000
2016/2017	16,410,000	3,010,000
Prior	60,734,000	61,266,000
Total amortized cost basis	227,988,000	234,933,000
Lease financing | Special mention
Credit quality
2020/2021	566,000	950,000
2019/2020	334,000	892,000
2018/2019	843,000	311,000
2017/2018	286,000	1,300,000
2016/2017	1,223,000	351,000
Prior	599,000	295,000
Total amortized cost basis	3,851,000	4,099,000
Lease financing | Substandard
Credit quality
2020/2021		2,708,000
2019/2020	2,714,000	1,677,000
2018/2019	1,673,000	327,000
2017/2018	293,000	1,141,000
2016/2017	1,107,000
Prior	522,000	526,000
Total amortized cost basis	6,309,000	6,379,000
Commercial Lending
Credit quality
2020/2021	585,772,000	1,429,127,000
2019/2020	1,347,526,000	1,342,590,000
2018/2019	1,345,285,000	1,027,719,000
2017/2018	967,048,000	679,422,000
2016/2017	634,947,000	428,830,000
Prior	1,574,078,000	1,121,767,000
Revolving Loans Amortized Cost Basis	1,010,528,000	1,332,983,000
Revolving Loans Converted to Term Loans Amortized Cost Basis	29,904,000	30,975,000
Total amortized cost basis	$ 7,495,088,000	$ 7,393,413,000