Loans, Allowance for Loan Losses and Credit Quality (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	$ 3,115,468	$ 3,077,026
PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,877,150	2,825,056
POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	106,584	118,479
DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	128,795	129,627
PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,939	3,864
DEFINITE LOSS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL
Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	702,486	687,511
Commercial and Industrial [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	665,025	647,984
Commercial and Industrial [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	15,851	16,420
Commercial and Industrial [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	20,735	21,979
Commercial and Industrial [Member] | PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	875	1,128
Commercial and Industrial [Member] | DEFINITE LOSS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL
Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,123,778	2,122,153
Commercial Real Estate [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,943,876	1,928,148
Commercial Real Estate [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	81,728	92,651
Commercial Real Estate [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	96,179	98,688
Commercial Real Estate [Member] | PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,995	2,666
Commercial Real Estate [Member] | DEFINITE LOSS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL
Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	211,984	188,768
Commercial Construction [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	198,476	177,693
Commercial Construction [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	5,977	6,195
Commercial Construction [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	7,531	4,880
Commercial Construction [Member] | PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL
Commercial Construction [Member] | DEFINITE LOSS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL
Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	77,220	78,594
Small Business [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	69,773	71,231
Small Business [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	3,028	3,213
Small Business [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	4,350	4,080
Small Business [Member] | PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	69	70
Small Business [Member] | DEFINITE LOSS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL