Loans, Allowance for Loan Losses and Credit Quality (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	$ 3,234,242	$ 3,077,026
Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	756,222	687,511
Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,166,281	2,122,153
Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	236,466	188,768
Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	75,273	78,594
PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	3,002,594	2,825,056
PASS [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	710,761	647,984
PASS [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,999,924	1,928,148
PASS [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	223,420	177,693
PASS [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	68,489	71,231
POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	106,860	118,479
POTENTIAL WEAKNESS [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	24,668	16,420
POTENTIAL WEAKNESS [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	71,371	92,651
POTENTIAL WEAKNESS [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	7,881	6,195
POTENTIAL WEAKNESS [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,940	3,213
DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	123,147	129,627
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	20,403	21,979
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	93,899	98,688
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	5,065	4,880
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	3,780	4,080
PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,641	3,864
PARTIAL LOSS PROBABLE [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	390	1,128
PARTIAL LOSS PROBABLE [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,087	2,666
PARTIAL LOSS PROBABLE [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	100
PARTIAL LOSS PROBABLE [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	64	70
DEFINITE LOSS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL
DEFINITE LOSS [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL
DEFINITE LOSS [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL
DEFINITE LOSS [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL
DEFINITE LOSS [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL