Loan Portfolio and Credit Quality Impaired Loans With and Without Related Allowance (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	$ 30,770	[1]	$ 42,345	[1]	$ 43,438	[1]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	19,672	[1]	19,345	[1]	18,905	[1]
Impaired Financing Receivable, Recorded Investment	50,442	[1]	61,690	[1]	62,343	[1]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	38,994		55,505		54,773
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	20,627		20,370		19,552
Impaired Financing Receivable, Unpaid Principal Balance	59,621		75,875		74,325
Impaired Financing Receivable, Related Allowance	4,104		2,151		4,185
Impaired Financing Receivable, Related Allowance	4,104		2,151		4,185
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	40,081		40,533		38,390
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	19,330		22,342		19,323
Impaired Financing Receivable, Average Recorded Investment	59,411		62,875		57,713
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	1,872		417		2,921
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	175		169		697
Impaired Financing Receivable, Interest Income, Cash Basis Method	2,047		586		3,618
Commercial and industrial [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	191	[1]	2,049	[1]	2,011	[1]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	941	[1]	1,082	[1]	891	[1]
Impaired Financing Receivable, Recorded Investment	1,132	[1]	3,131	[1]	2,902	[1]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	255		3,161		3,095
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	961		1,191		954
Impaired Financing Receivable, Unpaid Principal Balance	1,216		4,352		4,049
Impaired Financing Receivable, Related Allowance	78		74		91
Impaired Financing Receivable, Related Allowance	78		74		91
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,555		2,110		2,055
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	991		1,284		1,111
Impaired Financing Receivable, Average Recorded Investment	2,546		3,394		3,166
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	807		3		28
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	34		9		99
Impaired Financing Receivable, Interest Income, Cash Basis Method	841		12		127
Commercial real estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	19,059	[1]	29,346	[1]	21,500	[1]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	8,995	[1]	7,814	[1]	9,065	[1]
Impaired Financing Receivable, Recorded Investment	28,054	[1]	37,160	[1]	30,565	[1]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	25,414		40,065		28,700
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	9,423		8,243		9,493
Impaired Financing Receivable, Unpaid Principal Balance	34,837		48,308		38,193
Impaired Financing Receivable, Related Allowance	2,543		1,095		2,592
Impaired Financing Receivable, Related Allowance	2,543		1,095		2,592
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	20,753		30,416		24,921
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	9,036		8,453		7,925
Impaired Financing Receivable, Average Recorded Investment	29,789		38,869		32,846
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	894		269		2,483
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	92		91		379
Impaired Financing Receivable, Interest Income, Cash Basis Method	986		360		2,862
Construction and land [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,272	[1]	730	[1]	9,221	[1]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	2,200	[1]	2,724	[1]	2,200	[1]
Impaired Financing Receivable, Recorded Investment	3,472	[1]	3,454	[1]	11,421	[1]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	2,290		1,456		11,133
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	2,356		2,951		2,356
Impaired Financing Receivable, Unpaid Principal Balance	4,646		4,407		13,489
Impaired Financing Receivable, Related Allowance	172		239		172
Impaired Financing Receivable, Related Allowance	172		239		172
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	7,190		816		1,597
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	2,200		2,731		2,545
Impaired Financing Receivable, Average Recorded Investment	9,390		3,547		4,142
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	92		0		0
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0		0		0
Impaired Financing Receivable, Interest Income, Cash Basis Method	92		0		0
Residential [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	9,191	[1]	10,163	[1]	9,650	[1]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	7,536	[1]	7,725	[1]	6,749	[1]
Impaired Financing Receivable, Recorded Investment	16,727	[1]	17,888	[1]	16,399	[1]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	9,978		10,766		10,788
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	7,887		7,985		6,749
Impaired Financing Receivable, Unpaid Principal Balance	17,865		18,751		17,537
Impaired Financing Receivable, Related Allowance	1,311		743		1,330
Impaired Financing Receivable, Related Allowance	1,311		743		1,330
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	9,526		7,134		9,221
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	7,103		9,874		7,742
Impaired Financing Receivable, Average Recorded Investment	16,629		17,008		16,963
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	78		144		406
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	49		69		219
Impaired Financing Receivable, Interest Income, Cash Basis Method	127		213		625
Home equity [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	50	[1]	50	[1]	50	[1]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	[1]	0	[1]	0	[1]
Impaired Financing Receivable, Recorded Investment	50	[1]	50	[1]	50	[1]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	50		50		50
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0		0		0
Impaired Financing Receivable, Unpaid Principal Balance	50		50		50
Impaired Financing Receivable, Related Allowance	0		0		0
Impaired Financing Receivable, Related Allowance	0		0		0
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	50		50		50
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0		0		0
Impaired Financing Receivable, Average Recorded Investment	50		50		50
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	1		1		3
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0		0		0
Impaired Financing Receivable, Interest Income, Cash Basis Method	1		1		3
Consumer and other [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,007	[1]	7	[1]	1,006	[1]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	[1]	0	[1]	0	[1]
Impaired Financing Receivable, Recorded Investment	1,007	[1]	7	[1]	1,006	[1]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance	1,007		7		1,007
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance	0		0		0
Impaired Financing Receivable, Unpaid Principal Balance	1,007		7		1,007
Impaired Financing Receivable, Related Allowance	0		0		0
Impaired Financing Receivable, Related Allowance	0		0		0
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,007		7		546
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	0		0		0
Impaired Financing Receivable, Average Recorded Investment	1,007		7		546
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	0		0		1
Impaired Financing Receivable, with Related Allowance, Interest Income, Cash Basis Method	0		0		0
Impaired Financing Receivable, Interest Income, Cash Basis Method	$ 0		$ 0		$ 1

[1] Recorded investment represents the client loan balance net of historical charge-offs and historical nonaccrual interest paid, which was applied to principal.