Allowance for Loan Losses - Summary of Loans Based on Method for Determining Allowance (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	$ 8,704,392	$ 7,977,784
Allowance for loan losses	49,213	47,145	$ 47,145	$ 39,431	$ 37,897
New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	7,976,251	7,661,385
Allowance for loan losses	44,690			35,362
Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	728,141	316,399
Allowance for loan losses	1,113			1,344
Unallocated Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	0
Loans - Recorded investment, Collectively evaluated for impairment	8,704,392	7,977,784
Allowance for credit loss, Individually evaluated for impairment	0
Allowance for credit loss, Collectively evaluated for impairment	1,500	1,500
Allowance for loan losses	1,500
Total real estate loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	6,908,251	6,318,053
Total real estate loans | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	653	1,226
Loans - Recorded investment, Collectively evaluated for impairment	6,269,227	6,019,803
Loans - Recorded investment, ASC 310-30 loans	6,269,880	6,021,029
Allowance for credit loss, Individually evaluated for impairment	66	66
Allowance for credit loss, Collectively evaluated for impairment	27,855	27,736
Total real estate loans | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	4,609	4,655
Loans - Recorded investment, Collectively evaluated for impairment	428,255	147,354
Allowance for credit loss, Individually evaluated for impairment	129	129
Allowance for credit loss, Collectively evaluated for impairment	653	683
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	2,418,753	2,245,859
Allowance for loan losses	14,197		13,870	9,964	10,123
Commercial real estate | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	0	0
Loans - Recorded investment, Collectively evaluated for impairment	2,168,606	2,103,788
Loans - Recorded investment, ASC 310-30 loans	2,168,606	2,103,788
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	12,381	12,084
Allowance for loan losses	12,381			8,703
Commercial real estate | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	3,847	3,893
Loans - Recorded investment, Collectively evaluated for impairment	107,447	33,843
Allowance for credit loss, Individually evaluated for impairment	129	129
Allowance for credit loss, Collectively evaluated for impairment	234	209
Allowance for loan losses	337			344
Commercial real estate | Unallocated Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Allowance for loan losses	0
Owner-occupied commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	1,156,610	1,003,881
Allowance for loan losses	3,778		3,365	2,711	2,597
Owner-occupied commercial real estate | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	0	0
Loans - Recorded investment, Collectively evaluated for impairment	1,074,076	987,781
Loans - Recorded investment, ASC 310-30 loans	1,074,076	987,781
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	3,720	3,310
Allowance for loan losses	3,720			2,650
Owner-occupied commercial real estate | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	0	0
Loans - Recorded investment, Collectively evaluated for impairment	82,534	16,100
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	66	55
Allowance for loan losses	58			61
Owner-occupied commercial real estate | Unallocated Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Allowance for loan losses	0
1-4 single family residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	2,432,243	2,270,570
Allowance for loan losses	7,493		7,978	7,913	7,379
1-4 single family residential | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	524	1,096
Loans - Recorded investment, Collectively evaluated for impairment	2,232,267	2,184,266
Loans - Recorded investment, ASC 310-30 loans	2,232,791	2,185,362
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	7,281	7,769
Allowance for loan losses	7,281			7,639
1-4 single family residential | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	267	267
Loans - Recorded investment, Collectively evaluated for impairment	163,921	57,428
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	104	184
Allowance for loan losses	172			243
1-4 single family residential | Unallocated Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Allowance for loan losses	0
Construction, land and development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	796,152	703,518
Allowance for loan losses	4,288		4,345	4,918	4,677
Construction, land and development | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	0	0
Loans - Recorded investment, Collectively evaluated for impairment	732,551	684,462
Loans - Recorded investment, ASC 310-30 loans	732,551	684,462
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	4,109	4,164
Allowance for loan losses	4,109			4,569
Construction, land and development | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	0	0
Loans - Recorded investment, Collectively evaluated for impairment	32,413	5,889
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	39	36
Allowance for loan losses	36			44
Construction, land and development | Unallocated Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Allowance for loan losses	0
Home equity loans and lines of credit
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	104,493	94,225
Allowance for loan losses	616		674	726	648
Home equity loans and lines of credit | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	129	130
Loans - Recorded investment, Collectively evaluated for impairment	61,727	59,506
Loans - Recorded investment, ASC 310-30 loans	61,856	59,636
Allowance for credit loss, Individually evaluated for impairment	66	66
Allowance for credit loss, Collectively evaluated for impairment	364	409
Allowance for loan losses	430			450
Home equity loans and lines of credit | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	495	495
Loans - Recorded investment, Collectively evaluated for impairment	41,940	34,094
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	210	199
Allowance for loan losses	186			276
Home equity loans and lines of credit | Unallocated Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Allowance for loan losses	0
Total other loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	1,796,141	1,659,731
Total other loans | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	0	0
Loans - Recorded investment, Collectively evaluated for impairment	1,706,371	1,640,356
Loans - Recorded investment, ASC 310-30 loans	1,706,371	1,640,356
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	16,769	14,823
Total other loans | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	272	272
Loans - Recorded investment, Collectively evaluated for impairment	65,691	5,049
Allowance for credit loss, Individually evaluated for impairment	272	272
Allowance for credit loss, Collectively evaluated for impairment	59	47
Commercial and industrial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	1,771,845	1,652,065
Allowance for loan losses	17,114		15,141	12,953	12,245
Commercial and industrial | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	0	0
Loans - Recorded investment, Collectively evaluated for impairment	1,701,651	1,634,372
Loans - Recorded investment, ASC 310-30 loans	1,701,651	1,634,372
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	16,681	14,702
Allowance for loan losses	16,681			11,273
Commercial and industrial | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	272	272
Loans - Recorded investment, Collectively evaluated for impairment	47,488	4,790
Allowance for credit loss, Individually evaluated for impairment	272	272
Allowance for credit loss, Collectively evaluated for impairment	56	41
Allowance for loan losses	321			370
Commercial and industrial | Unallocated Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Allowance for loan losses	0
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	24,296	7,666
Allowance for loan losses	227		$ 272	246	$ 228
Consumer | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	0	0
Loans - Recorded investment, Collectively evaluated for impairment	4,720	5,984
Loans - Recorded investment, ASC 310-30 loans	4,720	5,984
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	88	121
Allowance for loan losses	88			78
Consumer | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, Individually evaluated for impairment	0	0
Loans - Recorded investment, Collectively evaluated for impairment	18,203	259
Allowance for credit loss, Individually evaluated for impairment	0	0
Allowance for credit loss, Collectively evaluated for impairment	3	6
Allowance for loan losses	3			6
Consumer | Unallocated Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Allowance for loan losses	0
ASC 310-30 Loans | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	229,314	159,069
Allowance for loan losses	1,910			2,725
ASC 310-30 Loans | Unallocated Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0
Allowance for loan losses	0
ASC 310-30 Loans | Total real estate loans | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Total real estate loans | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	205,507	145,015
Allowance for loan losses	1,662	1,618
ASC 310-30 Loans | Commercial real estate | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Commercial real estate | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	138,853	104,335
Allowance for loan losses	1,479	1,448		917
ASC 310-30 Loans | Owner-occupied commercial real estate | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Owner-occupied commercial real estate | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0	0
Allowance for loan losses	0	0		0
ASC 310-30 Loans | 1-4 single family residential | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | 1-4 single family residential | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	35,264	27,513
Allowance for loan losses	40	25		31
ASC 310-30 Loans | Construction, land and development | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Construction, land and development | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	31,188	13,167
Allowance for loan losses	143	145		305
ASC 310-30 Loans | Home equity loans and lines of credit | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Home equity loans and lines of credit | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	202	0
Allowance for loan losses	0	0		0
ASC 310-30 Loans | Total other loans | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Total other loans | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	23,807	14,054
Allowance for loan losses	248	271
ASC 310-30 Loans | Commercial and industrial | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Commercial and industrial | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	22,434	12,631
Allowance for loan losses	112	126		1,310
ASC 310-30 Loans | Consumer | New Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	0	0
Allowance for loan losses	0	0
ASC 310-30 Loans | Consumer | Acquired Loans
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans - Recorded investment, ASC 310-30 loans	1,373	1,423
Allowance for loan losses	$ 136	$ 145		$ 162