Loans Loans, analysis of purchased credit impaired loans (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Allowance	$ 83,968	$ 83,369	$ 75,646	$ 70,043
Loans and Leases Receivable, Net Amount	8,659,497	8,308,142
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	3,610,460	3,447,662
Real estate: One-to-four family residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	272,347	246,384
Loans and Leases Receivable, Allowance	607	593	701	599
Commercial and Multifamily Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	4,238,173	3,908,937
Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	4,510,520	4,155,321
One-to-Four Family Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	192,762	217,943
Commercial and Multifamily Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	163,103	284,928
Real Estate Construction Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	355,865	502,871
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	300,935	327,851
Loans and Leases Receivable, Allowance	4,455	5,301	$ 5,163	$ 3,534
Purchased Credit Impaired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	82,272	96,285
Valuation discount resulting from acquisition accounting	4,756	6,525
Loans and Leases Receivable, Allowance	2,844	3,611
Loans and Leases Receivable, Net Amount	74,672	86,149
Purchased Credit Impaired Loans [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	8,083	9,672
Purchased Credit Impaired Loans [Member] | Real estate: One-to-four family residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	8,453	9,848
Purchased Credit Impaired Loans [Member] | Commercial and Multifamily Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	56,752	66,340
Purchased Credit Impaired Loans [Member] | Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	65,205	76,188
Purchased Credit Impaired Loans [Member] | One-to-Four Family Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	0	153
Purchased Credit Impaired Loans [Member] | Commercial and Multifamily Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	0	507
Purchased Credit Impaired Loans [Member] | Real Estate Construction Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	0	660
Purchased Credit Impaired Loans [Member] | Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross, Carrying Amount	$ 8,984	$ 9,765