Loans, Net - Schedule of Loans by Portfolio and Segment (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 8,704,392	$ 7,977,784
Allowance for loan losses	(49,213)	(47,145)	$ (47,145)	$ (39,431)	$ (37,897)
Loans, net	8,655,179	7,930,639
Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	728,141	316,399
Allowance for loan losses	(1,113)			(1,344)
New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	7,976,251	7,661,385
Allowance for loan losses	(44,690)			(35,362)
Net deferred fees, costs, and premium and discount	(7,300)	(6,600)
Total real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,908,251	6,318,053
Total real estate loans | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,269,880	6,021,029
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,418,753	2,245,859
Allowance for loan losses	(14,197)		(13,870)	(9,964)	(10,123)
Commercial real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	(337)			(344)
Commercial real estate | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,168,606	2,103,788
Allowance for loan losses	(12,381)			(8,703)
Owner-occupied commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,156,610	1,003,881
Allowance for loan losses	(3,778)		(3,365)	(2,711)	(2,597)
Owner-occupied commercial real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	(58)			(61)
Owner-occupied commercial real estate | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,074,076	987,781
Allowance for loan losses	(3,720)			(2,650)
1-4 single family residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,432,243	2,270,570
Allowance for loan losses	(7,493)		(7,978)	(7,913)	(7,379)
1-4 single family residential | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	(172)			(243)
1-4 single family residential | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,232,791	2,185,362
Allowance for loan losses	(7,281)			(7,639)
Construction, land and development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	796,152	703,518
Allowance for loan losses	(4,288)		(4,345)	(4,918)	(4,677)
Construction, land and development | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	(36)			(44)
Construction, land and development | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	732,551	684,462
Allowance for loan losses	(4,109)			(4,569)
Home equity loans and lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	104,493	94,225
Allowance for loan losses	(616)		(674)	(726)	(648)
Home equity loans and lines of credit | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	(186)			(276)
Home equity loans and lines of credit | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	61,856	59,636
Allowance for loan losses	(430)			(450)
Total other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,796,141	1,659,731
Total other loans | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,706,371	1,640,356
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	24,296	7,666
Allowance for loan losses	(227)		(272)	(246)	(228)
Consumer | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	(3)			(6)
Consumer | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,720	5,984
Allowance for loan losses	(88)			(78)
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,771,845	1,652,065
Allowance for loan losses	(17,114)		$ (15,141)	(12,953)	$ (12,245)
Commercial and industrial | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	(321)			(370)
Commercial and industrial | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,701,651	1,634,372
Allowance for loan losses	(16,681)			(11,273)
ASC 310-30 Loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	229,314	159,069
Allowance for loan losses	(1,910)			(2,725)
ASC 310-30 Loans | Total real estate loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	205,507	145,015
Allowance for loan losses	(1,662)	(1,618)
ASC 310-30 Loans | Total real estate loans | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Commercial real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	138,853	104,335
Allowance for loan losses	(1,479)	(1,448)		(917)
ASC 310-30 Loans | Commercial real estate | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Owner-occupied commercial real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Allowance for loan losses	0	0		0
ASC 310-30 Loans | Owner-occupied commercial real estate | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | 1-4 single family residential | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	35,264	27,513
Allowance for loan losses	(40)	(25)		(31)
ASC 310-30 Loans | 1-4 single family residential | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Construction, land and development | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	31,188	13,167
Allowance for loan losses	(143)	(145)		(305)
ASC 310-30 Loans | Construction, land and development | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Home equity loans and lines of credit | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	202	0
Allowance for loan losses	0	0		0
ASC 310-30 Loans | Home equity loans and lines of credit | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Total other loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	23,807	14,054
Allowance for loan losses	(248)	(271)
ASC 310-30 Loans | Total other loans | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Consumer | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,373	1,423
Allowance for loan losses	(136)	(145)		(162)
ASC 310-30 Loans | Consumer | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Commercial and industrial | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	22,434	12,631
Allowance for loan losses	(112)	(126)		$ (1,310)
ASC 310-30 Loans | Commercial and industrial | New Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	0	0
Allowance for loan losses	0	0
Non-ASC 310-30 Loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	498,827	157,330
Non-ASC 310-30 Loans | Total real estate loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	432,864	152,009
Non-ASC 310-30 Loans | Commercial real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	111,294	37,736
Non-ASC 310-30 Loans | Owner-occupied commercial real estate | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	82,534	16,100
Non-ASC 310-30 Loans | 1-4 single family residential | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	164,188	57,695
Non-ASC 310-30 Loans | Construction, land and development | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	32,413	5,889
Non-ASC 310-30 Loans | Home equity loans and lines of credit | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	42,435	34,589
Non-ASC 310-30 Loans | Total other loans | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	65,963	5,321
Non-ASC 310-30 Loans | Consumer | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	18,203	259
Non-ASC 310-30 Loans | Commercial and industrial | Acquired Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 47,760	$ 5,062