Loans and reserve for credit losses (Narrative) (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Percentage of real estate related loans		74.50%		74.50%
Loans participated to third-parties		$ 43,800,000		$ 43,800,000			$ 34,500,000
Loans and Leases Receivable, gross		$ 1,626,590,000		$ 1,626,590,000			$ 1,492,540,000
Loans And Leases Receivable Gross, percent		100.00%		100.00%			100.00%
Percentage of Acquired Loans covered		13.20%		13.20%
Loan loss provision (recovery)		$ 0	$ 0	$ (2,000,000)	$ 0
Loans and Leases Receivable, allowance		23,501,000		23,501,000			$ 22,053,000
Total accruing loans which are contractually past due 90 days or more		47,000		47,000			54,000
Impaired loans, Total recorded balance		8,029,000		8,029,000			33,722,000
Troubled Debt Restructuring
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, allowance		100,000		100,000			100,000
Impaired loans, Total recorded balance		4,900,000		4,900,000			22,800,000
Loans and Leases Receivable, impaired, commitment to lend		0	0	0	0		0
Unallocated Financing Receivables
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, allowance		$ 2,294,000		$ 2,294,000			5,294,000
Originated Loans
Financing Receivable, Impaired [Line Items]
Percentage of real estate related loans		71.40%		71.40%
Loans and Leases Receivable, gross	[1],[2],[3]	$ 1,360,112,000		$ 1,360,112,000			$ 1,182,690,000
Loans And Leases Receivable Gross, percent	[3]	100.00%		100.00%			100.00%
Loans and Leases Receivable, allowance	[3]	$ 23,501,000		$ 23,501,000			$ 22,053,000
Acquired Covered Loans
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, gross	[4],[5],[6]	$ 35,285,000		$ 35,285,000			$ 40,191,000
Loans And Leases Receivable Gross, percent	[5]	100.00%		100.00%			100.00%
Loan Receivables
Financing Receivable, Impaired [Line Items]
Loan loss provision (recovery)		$ 0	0	$ (2,000,000)	0
Loans and Leases Receivable, allowance		23,501,000	20,471,000	23,501,000	20,471,000	$ 23,244,000	$ 22,053,000	$ 21,722,000	$ 20,857,000
Loan Receivables | Unallocated Financing Receivables
Financing Receivable, Impaired [Line Items]
Loan loss provision (recovery)		(65,000)	(88,000)	(3,000,000)	1,205,000
Loans and Leases Receivable, allowance		2,294,000	$ 1,919,000	2,294,000	$ 1,919,000	$ 2,359,000	5,294,000	$ 2,007,000	$ 714,000
Acquired and Acquired Covered Loans
Financing Receivable, Impaired [Line Items]
Assets, fair value adjustment				$ 6,000,000
Loans And Leases Receivable, Life of loans				10 years
Loans and Leases Receivable, gross	[6]	266,500,000		$ 266,500,000
Risk weighting for covered assets under loss sharing agreement, percentage				20.00%
Risk weighting for covered assets not under loss sharing agreement, percentage				100.00%
Substandard
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, gross		44,201,000		$ 44,201,000			38,635,000
Substandard | Originated Loans
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, gross	[1]	33,554,000		33,554,000			29,582,000
Substandard | Acquired Covered Loans
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, gross	[6]	$ 1,610,000		$ 1,610,000			$ 2,912,000
Loans And Leases Receivable, covered		15.10%		15.10%
Substandard | Acquired and Acquired Covered Loans
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, gross	[6]	$ 10,600,000		$ 10,600,000
Loans And Leases Receivable Gross, percent		4.00%		4.00%
Single Family | Acquired and Acquired Covered Loans
Financing Receivable, Impaired [Line Items]
Loss Sharing Agreement, term				10 years
Non-residential | Acquired and Acquired Covered Loans
Financing Receivable, Impaired [Line Items]
Loss Sharing Agreement, term				5 years
Loss Sharing Agreement, recovery period				3 years

[1] Originated loans are loans organically made through the Company's normal and customary origination process

[2] Originated loans are loans organically made through the Company's normal and customary origination process

[3] Originated loans are loans organically made through the Company's normal and customary origination process, including ARM purchases

[4] Acquired covered loans acquired in the acquisition of Home that are covered under FDIC loss share agreements

[5] Acquired covered loans are loans acquired in the acquisition of Home that are covered under FDIC loss share agreements.

[6] Acquired covered loans are loans in the Home portfolio that are covered under FDIC loss share agreements