Loans - Amount of Loans Receivable Held-for-Investment and Related Allowances Per Loan Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Allowance for loan losses:
Beginning Balance	$ 26,172	$ 25,284	$ 26,160	$ 24,595
Charge-offs	0	(290)	(64)	(317)
Recoveries	40	100	82	444
Provisions (credit)	670	511	704	883
Ending balance	26,882	25,605	26,882	25,605
Ending balance: individually evaluated for impairment	43		43		$ 82
Ending balance: collectively evaluated for impairment	26,839		26,839		26,078
Loans, net:
Loans held-for-investment, net	3,220,126		3,220,126		3,140,819
Ending balance: individually evaluated for impairment	20,090		20,090		21,085
Ending balance: collectively evaluated for impairment	3,200,036		3,200,036		3,119,734
Originated
Allowance for loan losses:
Beginning Balance	25,218	24,354	25,172	23,624
Charge-offs	0	(282)	(63)	(286)
Recoveries	38	98	74	440
Provisions (credit)	675	473	748	865
Ending balance	25,931	24,643	25,931	24,643
Ending balance: individually evaluated for impairment	43		43		45
Ending balance: collectively evaluated for impairment	25,888		25,888		25,127
Loans, net:
Loans held-for-investment, net	2,547,920		2,547,920		2,425,275
Ending balance: individually evaluated for impairment	19,146		19,146		19,542
Ending balance: collectively evaluated for impairment	2,528,774		2,528,774		2,405,733
Purchased Credit-Impaired
Allowance for loan losses:
Beginning Balance	951	896	951	896
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions (credit)	0	0	0	0
Ending balance	951	896	951	896
Ending balance: individually evaluated for impairment	0		0		0
Ending balance: collectively evaluated for impairment	951		951		951
Loans, net:
Loans held-for-investment, net	21,331		21,331		22,741
Ending balance: individually evaluated for impairment	0		0		0
Ending balance: collectively evaluated for impairment	21,331		21,331		22,741
Acquired Loans
Allowance for loan losses:
Beginning Balance	3	34	37	75
Charge-offs	0	(8)	(1)	(31)
Recoveries	2	2	8	4
Provisions (credit)	(5)	38	(44)	18
Ending balance	0	66	0	66
Ending balance: individually evaluated for impairment	0		0		37
Ending balance: collectively evaluated for impairment	0		0		0
Loans, net:
Loans held-for-investment, net	650,875		650,875		692,803
Ending balance: individually evaluated for impairment	944		944		1,543
Ending balance: collectively evaluated for impairment	649,931		649,931		691,260
Real Estate \| Commercial \| Originated
Allowance for loan losses:
Beginning Balance	5,213	5,231	5,196	5,432
Charge-offs	0	0	(3)	(4)
Recoveries	12	17	28	34
Provisions (credit)	493	(12)	497	(226)
Ending balance	5,718	5,236	5,718	5,236
Ending balance: individually evaluated for impairment	13		13		0
Ending balance: collectively evaluated for impairment	5,705		5,705		5,196
Loans, net:
Loans held-for-investment, net	500,051		500,051		445,781
Ending balance: individually evaluated for impairment	15,707		15,707		16,008
Ending balance: collectively evaluated for impairment	484,344		484,344		429,773
Real Estate \| One-to-Four Family \| Originated
Allowance for loan losses:
Beginning Balance	455	649	503	664
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions (credit)	(71)	(99)	(119)	(114)
Ending balance	384	550	384	550
Ending balance: individually evaluated for impairment	18		18		38
Ending balance: collectively evaluated for impairment	366		366		465
Loans, net:
Loans held-for-investment, net	101,354		101,354		101,650
Ending balance: individually evaluated for impairment	1,947		1,947		1,996
Ending balance: collectively evaluated for impairment	99,407		99,407		99,654
Real Estate \| Construction and Land \| Originated
Allowance for loan losses:
Beginning Balance	463	165	610	172
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions (credit)	(25)	64	(172)	57
Ending balance	438	229	438	229
Ending balance: individually evaluated for impairment	0		0		0
Ending balance: collectively evaluated for impairment	438		438		610
Loans, net:
Loans held-for-investment, net	27,048		27,048		34,620
Ending balance: individually evaluated for impairment	0		0		0
Ending balance: collectively evaluated for impairment	27,048		27,048		34,620
Real Estate \| Multifamily \| Originated
Allowance for loan losses:
Beginning Balance	17,412	16,184	17,374	14,952
Charge-offs	0	(178)	0	(178)
Recoveries	26	0	26	278
Provisions (credit)	165	630	203	1,584
Ending balance	17,603	16,636	17,603	16,636
Ending balance: individually evaluated for impairment	0		0		0
Ending balance: collectively evaluated for impairment	17,603		17,603		17,374
Loans, net:
Loans held-for-investment, net	1,803,834		1,803,834		1,739,220
Ending balance: individually evaluated for impairment	1,275		1,275		1,310
Ending balance: collectively evaluated for impairment	1,802,559		1,802,559		1,737,910
Real Estate \| Home equity and lines of credit \| Originated
Allowance for loan losses:
Beginning Balance	225	492	122	588
Charge-offs	0	(104)	(60)	(104)
Recoveries	0	64	0	64
Provisions (credit)	54	(89)	217	(185)
Ending balance	279	363	279	363
Ending balance: individually evaluated for impairment	10		10		4
Ending balance: collectively evaluated for impairment	269		269		118
Loans, net:
Loans held-for-investment, net	74,324		74,324		67,679
Ending balance: individually evaluated for impairment	65		65		69
Ending balance: collectively evaluated for impairment	74,259		74,259		67,610
Commercial and Industrial \| Originated
Allowance for loan losses:
Beginning Balance	1,337	1,561	1,273	1,720
Charge-offs	0	0	0	0
Recoveries	0	17	20	64
Provisions (credit)	65	(46)	109	(252)
Ending balance	1,402	1,532	1,402	1,532
Ending balance: individually evaluated for impairment	2		2		3
Ending balance: collectively evaluated for impairment	1,400		1,400		1,270
Loans, net:
Loans held-for-investment, net	39,776		39,776		34,893
Ending balance: individually evaluated for impairment	152		152		159
Ending balance: collectively evaluated for impairment	39,624		39,624		34,734
Other \| Originated
Allowance for loan losses:
Beginning Balance	113	72	94	96
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions (credit)	(6)	25	13	1
Ending balance	107	97	107	97
Ending balance: individually evaluated for impairment	0		0		0
Ending balance: collectively evaluated for impairment	107		107		94
Loans, net:
Loans held-for-investment, net	1,533		1,533		1,432
Ending balance: individually evaluated for impairment	0		0		0
Ending balance: collectively evaluated for impairment	1,533		1,533		$ 1,432
Unallocated \| Originated
Allowance for loan losses:
Beginning Balance	0	0	0	0
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provisions (credit)	0	0	0	0
Ending balance	$ 0	$ 0	$ 0	$ 0

Originated loans, net.

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Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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The balance of financing receivables that were collectively evaluated for impairment.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount of expense related to estimated loss from loan and lease transactions.

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