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Loans, Allowance for Loan Losses and Credit Quality (Internal Risk-Rating Categories for the Commercial Portfolio) (Details) - USD ($) | 9 Months Ended |
--- | --- | ---
Sep. 30, 2017 | Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Significant Advanced Considered For Risk Rating Change | $ 50,000 |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 4,471,605,000 | $ 4,355,968,000
Commercial and Industrial [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 858,522,000 | 902,053,000
Commercial Real Estate [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 3,087,160,000 | 3,010,798,000
Commercial Construction [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 395,267,000 | 320,391,000
Small Business [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 130,656,000 | 122,726,000
PASS [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 4,255,483,000 | 4,097,798,000
PASS [Member] | Commercial and Industrial [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 764,946,000 | 783,825,000
PASS [Member] | Commercial Real Estate [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 2,968,237,000 | 2,876,570,000
PASS [Member] | Commercial Construction [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 393,836,000 | 317,099,000
PASS [Member] | Small Business [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 128,464,000 | 120,304,000
POTENTIAL WEAKNESS [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 98,239,000 | 134,039,000
POTENTIAL WEAKNESS [Member] | Commercial and Industrial [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 23,477,000 | 46,176,000
POTENTIAL WEAKNESS [Member] | Commercial Real Estate [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 73,219,000 | 84,641,000
POTENTIAL WEAKNESS [Member] | Commercial Construction [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 0 | 1,363,000
POTENTIAL WEAKNESS [Member] | Small Business [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 1,543,000 | 1,859,000
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 111,173,000 | 121,640,000
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial and Industrial [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 63,856,000 | 71,991,000
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial Real Estate [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 45,240,000 | 47,164,000
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial Construction [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 1,431,000 | 1,929,000
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Small Business [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 646,000 | 556,000
PARTIAL LOSS PROBABLE [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 6,710,000 | 2,491,000
PARTIAL LOSS PROBABLE [Member] | Commercial and Industrial [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 6,243,000 | 61,000
PARTIAL LOSS PROBABLE [Member] | Commercial Real Estate [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 464,000 | 2,423,000
PARTIAL LOSS PROBABLE [Member] | Commercial Construction [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 0 | 0
PARTIAL LOSS PROBABLE [Member] | Small Business [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 3,000 | 7,000
DEFINITE LOSS [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 0 | 0
DEFINITE LOSS [Member] | Commercial and Industrial [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 0 | 0
DEFINITE LOSS [Member] | Commercial Real Estate [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 0 | 0
DEFINITE LOSS [Member] | Commercial Construction [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | 0 | 0
DEFINITE LOSS [Member] | Small Business [Member] |  |
Internal risk-rating categories for the Company's commercial portfolio |  |
TOTAL | $ 0 | $ 0

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