Loans and reserve for credit losses (Narrative) (Details) - USD ($)				3 Months Ended								5 Months Ended	12 Months Ended
		Aug. 01, 2016	May 16, 2014	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of real estate related loans				78.20%								78.20%	78.20%
Loans participated to third-parties				$ 128,800,000				$ 44,200,000				$ 128,800,000	$ 128,800,000	$ 44,200,000
Purchased loan participations				145,300,000				179,200,000				145,300,000	145,300,000	179,200,000
Loans receivable				2,104,412,000				1,687,929,000				2,104,412,000	2,104,412,000	1,687,929,000
Loan loss recovery				0	$ 0	$ 0	$ 0	(2,000,000)	$ 0	$ 0	$ (2,000,000)		0	(4,000,000)	$ 0
Total accruing loans which are contractually past due 90 days or more				17,000				68,000				17,000	17,000	68,000
Impaired loans, total recorded balance				7,674,000				6,942,000				7,674,000	7,674,000	6,942,000
Interest income for cash payment on impaired loans													1,100,000	600,000
Loans and leases receivable, allowance				25,290,000				24,415,000				25,290,000	25,290,000	24,415,000
Troubled Debt Restructuring
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans, total recorded balance				0				800,000				0	0	800,000
Loans and leases receivable, allowance				0				0				0	0	0
Loans and leases receivable, impaired, commitment to lend				0				0				0	0	0
Unallocated
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, allowance				$ 1,588,000				2,476,000				$ 1,588,000	1,588,000	2,476,000
Special Mention and Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in loans and leases receivable													$ (26,500,000)
Originated Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of real estate related loans				76.40%								76.40%	76.40%
Loans receivable	[1]			$ 1,819,334,000				1,452,978,000				$ 1,819,334,000	$ 1,819,334,000	1,452,978,000
Loans and leases receivable, allowance	[1]			25,290,000				$ 24,415,000				25,290,000	25,290,000	$ 24,415,000
Originated Loans | Special Mention and Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in loans and leases receivable													(10,200,000)
Acquired and Acquired Covered Loans, Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable				$ 285,100,000								$ 285,100,000	$ 285,100,000
Percentage of acquired loans covered				7.60%								7.60%	7.60%
Risk weighting received for covered assets under loss sharing agreement													20.00%
Risk weighting received for covered assets not under loss sharing agreement													100.00%
Acquired and Acquired Covered Loans, Receivable | Non-residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loss sharing agreement, term													5 years
Loss sharing agreement, recovery period													3 years
Acquired and Acquired Covered Loans, Receivable | Single Family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loss sharing agreement, term													10 years
Acquired and Acquired Covered Loans, Receivable | Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable				$ 8,000,000								$ 8,000,000	$ 8,000,000
Total loans, percent				2.80%								2.80%	2.80%
Acquired and Acquired Covered Loans, Receivable | Prime Pacific Financial Services
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in acquired and acquired covered loans		$ 2,500,000										$ (1,700,000)
Life of loans													10 years
Acquired and Acquired Covered Loans, Receivable | Home Federal Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increase (decrease) in acquired and acquired covered loans			$ 6,000,000										$ (1,600,000)
Life of loans													10 years
Acquired Covered Loans, Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans receivable net reported amount covered				$ 21,600,000								$ 21,600,000	$ 21,600,000

[1] Loans organically made through the Company’s normal and customary origination process, including ARM purchases.