Loans, Allowance for Loan Losses and Credit Quality (Internal Risk-Rating Categories for the Commercial Portfolio) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	$ 3,873,226	$ 3,559,403
Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	873,105	860,839
Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,630,062	2,347,323
Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	278,692	265,994
Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	91,367	85,247
PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	3,647,983	3,327,638
PASS [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	803,026	801,578
PASS [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,488,514	2,196,109
PASS [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	268,628	248,696
PASS [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	87,815	81,255
POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	140,044	138,570
POTENTIAL WEAKNESS [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	50,448	37,802
POTENTIAL WEAKNESS [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	77,276	82,372
POTENTIAL WEAKNESS [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	9,530	15,464
POTENTIAL WEAKNESS [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,790	2,932
DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	83,827	90,595
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	19,540	20,241
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	63,069	67,571
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	534	1,834
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	684	949
PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,372	2,600
PARTIAL LOSS PROBABLE [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	91	1,218
PARTIAL LOSS PROBABLE [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,203	1,271
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	78	111
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