Basis of presentation and summary of significant accounting policies (Details) - USD ($)		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounting Policies [Line Items]
Transfer to other real estate		$ 1,600,000	$ 200,000	$ 2,100,000
Transfer from fixed assets		400,000
Interest paid		8,100,000	8,100,000	3,000,000
Income taxes paid		1,100,000	0	100,000
Trading securities		$ 0	0	0
Threshold period past due for financing receivables		90 days
Loans and leases receivable, allowance		$ 24,415,000	22,053,000
MSRs		2,186,000	2,248,000	2,232,000
Bank owned life insurance		54,450,000	53,449,000
Other real estate owned (OREO), net		3,274,000	3,309,000	3,144,000	$ 6,552,000
Advertising expense		600,000	900,000	1,000,000
Deferred tax assets, valuation allowance		74,000	78,000	100,000	41,700,000
Previously written off section 382 deferred tax benefits				8,500,000
Swap fee income		2,533,000	1,847,000	430,000
Interest rate swap derivatives		8,646,000
Derivative notional amount		169,700,000	82,900,000
Assets held-in-trust		$ 57,000,000	$ 58,500,000
Preferred stock, shares authorized		5,000,000	5,000,000
Federal Home Loan Bank Stock		$ 3,000,000	$ 25,646,000
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible, net		$ 6,863,000	$ 7,683,000
Preferred Stock, Shares Issued		0	0
Preferred Stock, Shares Outstanding		0	0
One-to-Four Family Loans
Accounting Policies [Line Items]
Threshold period for one-to-four family loans to be deemed current		90 days
Unallocated
Accounting Policies [Line Items]
Loans and leases receivable, allowance		$ 2,476,000	$ 5,294,000
Separate Account BOLI
Accounting Policies [Line Items]
Bank owned life insurance		28,600,000	28,300,000
General Account BOLI
Accounting Policies [Line Items]
Bank owned life insurance		25,900,000	25,100,000
Loans Receivable
Accounting Policies [Line Items]
Loans and leases receivable, allowance		24,415,000	22,053,000	20,857,000	27,261,000
Loans Receivable | Unallocated
Accounting Policies [Line Items]
Loans and leases receivable, allowance		2,476,000	5,294,000	714,000	1,087,000
Decrease in loans and leases receivable allowance		2,800,000
Unfunded Lending Commitments
Accounting Policies [Line Items]
Loans and leases receivable, allowance		440,000	440,000	440,000	440,000
Unfunded Lending Commitments | Unallocated
Accounting Policies [Line Items]
Loans and leases receivable, allowance		0	0	0	$ 0
Core Deposits
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible, net		6,863,000	7,683,000	$ 529,000
Interest Rate Swap
Accounting Policies [Line Items]
Interest rate swap derivatives	[1]	8,600,000	4,800,000
Interest rate swap derivatives		$ 8,600,000	$ 4,800,000

[1] Included in other assets on the consolidated balance sheet