Loans, Allowance for Credit Losses, and Credit Quality Loans by Past Due Status (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Summarized details of Loans
30-59 Days Past Due	$ 32,588,000	$ 39,373,000
60-89 Days Past Due	11,952,000	22,705,000
90 Days or More Past Due	54,337,000	64,922,000
Total Past Due	98,877,000	127,000,000
Current	17,880,155,000	17,466,846,000
Total loans	17,979,032,000	17,593,846,000
Accruing loans past due 90 days or more	2,000,000	2,000,000
Percent of current nonaccrual loans	57.00%	54.00%
Commercial And Industrial Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	7,109,000	5,338,000
60-89 Days Past Due	3,851,000	10,908,000
90 Days or More Past Due	10,132,000	10,408,000
Total Past Due	21,092,000	26,654,000
Current	6,119,328,000	5,879,248,000
Total loans	6,140,420,000	5,905,902,000
Commercial Real Estate Owner Occupied Portfolio [Member]
Summarized details of Loans
30-59 Days Past Due	4,124,000	11,626,000
60-89 Days Past Due	185,000	2,240,000
90 Days or More Past Due	8,644,000	8,596,000
Total Past Due	12,953,000	22,462,000
Current	990,932,000	985,475,000
Total loans	1,003,885,000	1,007,937,000
Finance Leases Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	0	0
60-89 Days Past Due	0	0
90 Days or More Past Due	513,000	513,000
Total Past Due	513,000	513,000
Current	48,983,000	51,016,000
Total loans	49,496,000	51,529,000
Commercial And Business Lending [Member]
Summarized details of Loans
30-59 Days Past Due	11,233,000	16,964,000
60-89 Days Past Due	4,036,000	13,148,000
90 Days or More Past Due	19,289,000	19,517,000
Total Past Due	34,558,000	49,629,000
Current	7,159,243,000	6,915,739,000
Total loans	7,193,801,000	6,965,368,000
Commercial Real Estate Investor Portfolio Segment [Member]
Summarized details of Loans
30-59 Days Past Due	1,942,000	2,569,000
60-89 Days Past Due	448,000	955,000
90 Days or More Past Due	5,395,000	12,765,000
Total Past Due	7,785,000	16,289,000
Current	3,079,195,000	3,040,196,000
Total loans	3,086,980,000	3,056,485,000
Commercial Real Estate Construction Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	1,667,000	1,038,000
60-89 Days Past Due	173,000	106,000
90 Days or More Past Due	872,000	798,000
Total Past Due	2,712,000	1,942,000
Current	1,016,859,000	1,007,014,000
Total loans	1,019,571,000	1,008,956,000
Commercial Real Estate Lending [Member]
Summarized details of Loans
30-59 Days Past Due	3,609,000	3,607,000
60-89 Days Past Due	621,000	1,061,000
90 Days or More Past Due	6,267,000	13,563,000
Total Past Due	10,497,000	18,231,000
Current	4,096,054,000	4,047,210,000
Total loans	4,106,551,000	4,065,441,000
Commercial Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	14,842,000	20,571,000
60-89 Days Past Due	4,657,000	14,209,000
90 Days or More Past Due	25,556,000	33,080,000
Total Past Due	45,055,000	67,860,000
Current	11,255,297,000	10,962,949,000
Total loans	11,300,352,000	11,030,809,000
Home Equity [Member]
Summarized details of Loans
30-59 Days Past Due	9,955,000	9,652,000
60-89 Days Past Due	3,200,000	4,852,000
90 Days or More Past Due	9,663,000	10,654,000
Total Past Due	22,818,000	25,158,000
Current	1,560,796,000	1,610,900,000
Total loans	1,583,614,000	1,636,058,000
Installment and Credit Cards [Member]
Summarized details of Loans
30-59 Days Past Due	1,213,000	1,282,000
60-89 Days Past Due	673,000	785,000
90 Days or More Past Due	1,587,000	1,458,000
Total Past Due	3,473,000	3,525,000
Current	433,019,000	450,694,000
Total loans	436,492,000	454,219,000
Residential, Prime, Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	6,578,000	7,868,000
60-89 Days Past Due	3,422,000	2,859,000
90 Days or More Past Due	17,531,000	19,730,000
Total Past Due	27,531,000	30,457,000
Current	4,631,043,000	4,442,303,000
Total loans	4,658,574,000	4,472,760,000
Consumer Loan [Member]
Summarized details of Loans
30-59 Days Past Due	17,746,000	18,802,000
60-89 Days Past Due	7,295,000	8,496,000
90 Days or More Past Due	28,781,000	31,842,000
Total Past Due	53,822,000	59,140,000
Current	6,624,858,000	6,503,897,000
Total loans	6,678,680,000	6,563,037,000
Accruing Loans [Member]
Summarized details of Loans
30-59 Days Past Due	18,333,000	26,621,000
60-89 Days Past Due	2,994,000	16,507,000
90 Days or More Past Due	1,715,000	1,623,000
Total Past Due	23,042,000	44,751,000
Current	17,781,644,000	17,371,682,000
Total loans	17,804,686,000	17,416,433,000
Accruing Loans [Member] | Commercial And Industrial Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	1,281,000	4,466,000
60-89 Days Past Due	436,000	10,281,000
90 Days or More Past Due	197,000	254,000
Total Past Due	1,914,000	15,001,000
Current	6,076,886,000	5,841,238,000
Total loans	6,078,800,000	5,856,239,000
Accruing Loans [Member] | Commercial Real Estate Owner Occupied Portfolio [Member]
Summarized details of Loans
30-59 Days Past Due	1,849,000	8,429,000
60-89 Days Past Due	0	2,199,000
90 Days or More Past Due	0	0
Total Past Due	1,849,000	10,628,000
Current	980,175,000	971,484,000
Total loans	982,024,000	982,112,000
Accruing Loans [Member] | Finance Leases Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	0	0
60-89 Days Past Due	0	0
90 Days or More Past Due	0	0
Total Past Due	0	0
Current	47,776,000	49,728,000
Total loans	47,776,000	49,728,000
Accruing Loans [Member] | Commercial And Business Lending [Member]
Summarized details of Loans
30-59 Days Past Due	3,130,000	12,895,000
60-89 Days Past Due	436,000	12,480,000
90 Days or More Past Due	197,000	254,000
Total Past Due	3,763,000	25,629,000
Current	7,104,837,000	6,862,450,000
Total loans	7,108,600,000	6,888,079,000
Accruing Loans [Member] | Commercial Real Estate Investor Portfolio Segment [Member]
Summarized details of Loans
30-59 Days Past Due	1,767,000	712,000
60-89 Days Past Due	448,000	496,000
90 Days or More Past Due	0	0
Total Past Due	2,215,000	1,208,000
Current	3,071,023,000	3,032,592,000
Total loans	3,073,238,000	3,033,800,000
Accruing Loans [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	317,000	951,000
60-89 Days Past Due	0	33,000
90 Days or More Past Due	0	0
Total Past Due	317,000	984,000
Current	1,013,831,000	1,002,573,000
Total loans	1,014,148,000	1,003,557,000
Accruing Loans [Member] | Commercial Real Estate Lending [Member]
Summarized details of Loans
30-59 Days Past Due	2,084,000	1,663,000
60-89 Days Past Due	448,000	529,000
90 Days or More Past Due	0	0
Total Past Due	2,532,000	2,192,000
Current	4,084,854,000	4,035,165,000
Total loans	4,087,386,000	4,037,357,000
Accruing Loans [Member] | Commercial Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	5,214,000	14,558,000
60-89 Days Past Due	884,000	13,009,000
90 Days or More Past Due	197,000	254,000
Total Past Due	6,295,000	27,821,000
Current	11,189,691,000	10,897,615,000
Total loans	11,195,986,000	10,925,436,000
Accruing Loans [Member] | Home Equity [Member]
Summarized details of Loans
30-59 Days Past Due	8,637,000	8,037,000
60-89 Days Past Due	1,371,000	2,546,000
90 Days or More Past Due	85,000	52,000
Total Past Due	10,093,000	10,635,000
Current	1,553,094,000	1,603,682,000
Total loans	1,563,187,000	1,614,317,000
Accruing Loans [Member] | Installment and Credit Cards [Member]
Summarized details of Loans
30-59 Days Past Due	1,180,000	1,186,000
60-89 Days Past Due	638,000	746,000
90 Days or More Past Due	1,433,000	1,317,000
Total Past Due	3,251,000	3,249,000
Current	432,726,000	450,357,000
Total loans	435,977,000	453,606,000
Accruing Loans [Member] | Residential, Prime, Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	3,302,000	2,840,000
60-89 Days Past Due	101,000	206,000
90 Days or More Past Due	0	0
Total Past Due	3,403,000	3,046,000
Current	4,606,133,000	4,420,028,000
Total loans	4,609,536,000	4,423,074,000
Accruing Loans [Member] | Consumer Loan [Member]
Summarized details of Loans
30-59 Days Past Due	13,119,000	12,063,000
60-89 Days Past Due	2,110,000	3,498,000
90 Days or More Past Due	1,518,000	1,369,000
Total Past Due	16,747,000	16,930,000
Current	6,591,953,000	6,474,067,000
Total loans	6,608,700,000	6,490,997,000
Nonaccrual Loan [Member]
Summarized details of Loans
30-59 Days Past Due	14,255,000	12,752,000
60-89 Days Past Due	8,958,000	6,198,000
90 Days or More Past Due	52,622,000	63,299,000
Total Past Due	75,835,000	82,249,000
Current	98,511,000	95,164,000
Total loans	174,346,000	177,413,000
Nonaccrual Loan [Member] | Commercial And Industrial Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	5,828,000	872,000
60-89 Days Past Due	3,415,000	627,000
90 Days or More Past Due	9,935,000	10,154,000
Total Past Due	19,178,000	11,653,000
Current	42,442,000	38,010,000
Total loans	61,620,000	49,663,000
Nonaccrual Loan [Member] | Commercial Real Estate Owner Occupied Portfolio [Member]
Summarized details of Loans
30-59 Days Past Due	2,275,000	3,197,000
60-89 Days Past Due	185,000	41,000
90 Days or More Past Due	8,644,000	8,596,000
Total Past Due	11,104,000	11,834,000
Current	10,757,000	13,991,000
Total loans	21,861,000	25,825,000
Nonaccrual Loan [Member] | Finance Leases Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	0	0
60-89 Days Past Due	0	0
90 Days or More Past Due	513,000	513,000
Total Past Due	513,000	513,000
Current	1,207,000	1,288,000
Total loans	1,720,000	1,801,000
Nonaccrual Loan [Member] | Commercial And Business Lending [Member]
Summarized details of Loans
30-59 Days Past Due	8,103,000	4,069,000
60-89 Days Past Due	3,600,000	668,000
90 Days or More Past Due	19,092,000	19,263,000
Total Past Due	30,795,000	24,000,000
Current	54,406,000	53,289,000
Total loans	85,201,000	77,289,000
Nonaccrual Loan [Member] | Commercial Real Estate Investor Portfolio Segment [Member]
Summarized details of Loans
30-59 Days Past Due	175,000	1,857,000
60-89 Days Past Due	0	459,000
90 Days or More Past Due	5,395,000	12,765,000
Total Past Due	5,570,000	15,081,000
Current	8,172,000	7,604,000
Total loans	13,742,000	22,685,000
Nonaccrual Loan [Member] | Commercial Real Estate Construction Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	1,350,000	87,000
60-89 Days Past Due	173,000	73,000
90 Days or More Past Due	872,000	798,000
Total Past Due	2,395,000	958,000
Current	3,028,000	4,441,000
Total loans	5,423,000	5,399,000
Nonaccrual Loan [Member] | Commercial Real Estate Lending [Member]
Summarized details of Loans
30-59 Days Past Due	1,525,000	1,944,000
60-89 Days Past Due	173,000	532,000
90 Days or More Past Due	6,267,000	13,563,000
Total Past Due	7,965,000	16,039,000
Current	11,200,000	12,045,000
Total loans	19,165,000	28,084,000
Nonaccrual Loan [Member] | Commercial Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	9,628,000	6,013,000
60-89 Days Past Due	3,773,000	1,200,000
90 Days or More Past Due	25,359,000	32,826,000
Total Past Due	38,760,000	40,039,000
Current	65,606,000	65,334,000
Total loans	104,366,000	105,373,000
Nonaccrual Loan [Member] | Home Equity [Member]
Summarized details of Loans
30-59 Days Past Due	1,318,000	1,615,000
60-89 Days Past Due	1,829,000	2,306,000
90 Days or More Past Due	9,578,000	10,602,000
Total Past Due	12,725,000	14,523,000
Current	7,702,000	7,218,000
Total loans	20,427,000	21,741,000
Nonaccrual Loan [Member] | Installment and Credit Cards [Member]
Summarized details of Loans
30-59 Days Past Due	33,000	96,000
60-89 Days Past Due	35,000	39,000
90 Days or More Past Due	154,000	141,000
Total Past Due	222,000	276,000
Current	293,000	337,000
Total loans	515,000	613,000
Nonaccrual Loan [Member] | Residential, Prime, Financing Receivable [Member]
Summarized details of Loans
30-59 Days Past Due	3,276,000	5,028,000
60-89 Days Past Due	3,321,000	2,653,000
90 Days or More Past Due	17,531,000	19,730,000
Total Past Due	24,128,000	27,411,000
Current	24,910,000	22,275,000
Total loans	49,038,000	49,686,000
Nonaccrual Loan [Member] | Consumer Loan [Member]
Summarized details of Loans
30-59 Days Past Due	4,627,000	6,739,000
60-89 Days Past Due	5,185,000	4,998,000
90 Days or More Past Due	27,263,000	30,473,000
Total Past Due	37,075,000	42,210,000
Current	32,905,000	29,830,000
Total loans	$ 69,980,000	$ 72,040,000