Loans, Allowance for Loan Losses and Credit Quality (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	$ 2,847,631	$ 2,630,783
PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,611,091	2,340,719
POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	107,207	169,874
DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	126,867	116,295
PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,466	3,895
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	653,861	575,716
Commercial and Industrial [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	615,349	528,798
Commercial and Industrial [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	19,584	33,313
Commercial and Industrial [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	17,541	12,683
Commercial and Industrial [Member] | PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,387	922
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	1,939,245	1,847,654
Commercial Real Estate [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,759,857	1,626,745
Commercial Real Estate [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	77,791	124,661
Commercial Real Estate [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	100,602	93,438
Commercial Real Estate [Member] | PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	995	2,810
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	175,731	128,904
Commercial Construction [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	164,545	114,633
Commercial Construction [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	6,159	7,859
Commercial Construction [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	5,027	6,412
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	78,794	78,509
Small Business [Member] | PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	71,340	70,543
Small Business [Member] | POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	3,673	4,041
Small Business [Member] | DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	3,697	3,762
Small Business [Member] | PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	84	163
Small Business [Member] | DEFINITE LOSS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL