Loans, Allowance for Loan Losses and Credit Quality (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	$ 3,202,178	$ 3,077,026
PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,967,679	2,825,056
POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	101,222	118,479
DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	131,002	129,627
PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,275	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	742,343	687,511
Commercial and Industrial [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	704,065	647,984
Commercial and Industrial [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	17,088	16,420
Commercial and Industrial [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	20,410	21,979
Commercial and Industrial [Member] | PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	780	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	2,150,833	2,122,153
Commercial Real Estate [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,976,410	1,928,148
Commercial Real Estate [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	74,143	92,651
Commercial Real Estate [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	98,818	98,688
Commercial Real Estate [Member] | PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,462	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	231,719	188,768
Commercial Construction [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	217,096	177,693
Commercial Construction [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	6,955	6,195
Commercial Construction [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	7,668	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	77,283	78,594
Small Business [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	70,108	71,231
Small Business [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	3,036	3,213
Small Business [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	4,106	4,080
Small Business [Member] | PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	33	70
Small Business [Member] | DEFINITE LOSS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL