Loans, Leases and Allowance for Credit Losses - Summary of Impairment Method Information Related to Loans and Allowance for Credit Losses (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	$ 9,598	$ 19,315
Impaired loans with no allowance recorded	87,994	79,239
Total loans individually evaluated for impairment	97,592	98,554
Loans collectively evaluated for impairment	15,352,070	14,879,626
Impaired Financing Receivable, Recorded Investment	97,592	98,554
Total recorded investment	15,560,453	15,093,935
Impaired loans with an allowance recorded	12,423	20,795
Impaired loans with no allowance recorded	167,192	156,789
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	179,615	177,584
Loans collectively evaluated for impairment	15,352,070	14,879,626
Financing Receivable Unpaid Principal Balance	15,671,560	15,202,135
Impaired loans with an allowance recorded	5,562	5,606
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	5,562	5,606
Loans collectively evaluated for impairment	138,268	132,813
Total loans held for investment	144,659	140,050
Owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	8,107	10,430
Total loans individually evaluated for impairment	8,107	10,430
Loans collectively evaluated for impairment	2,248,803	2,221,614
Total recorded investment	2,264,650	2,241,613
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	15,029	17,459
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	15,029	17,459
Loans collectively evaluated for impairment	2,248,803	2,221,614
Financing Receivable Unpaid Principal Balance	2,273,777	2,251,692
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	14,475	13,884
Total loans held for investment	14,475	13,884
Non-owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	17,654	21,250
Total loans individually evaluated for impairment	17,654	21,250
Loans collectively evaluated for impairment	3,805,229	3,777,219
Total recorded investment	3,925,301	3,904,011
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	24,431	28,028
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	24,431	28,028
Loans collectively evaluated for impairment	3,805,229	3,777,219
Financing Receivable Unpaid Principal Balance	3,954,463	3,933,687
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	17,566	16,135
Total loans held for investment	18,393	17,764
Commercial and industrial [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	9,425	19,315
Impaired loans with no allowance recorded	34,034	14,842
Total loans individually evaluated for impairment	43,459	34,157
Loans collectively evaluated for impairment	6,900,885	6,807,181
Total recorded investment	6,944,381	6,841,381
Impaired loans with an allowance recorded	12,250	20,795
Impaired loans with no allowance recorded	63,541	42,261
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	75,791	63,056
Loans collectively evaluated for impairment	6,900,885	6,807,181
Financing Receivable Unpaid Principal Balance	6,981,088	6,873,383
Impaired loans with an allowance recorded	5,389	5,606
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	5,389	5,606
Loans collectively evaluated for impairment	77,487	76,919
Total loans held for investment	82,878	82,527
Residential real estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	173	0
Impaired loans with no allowance recorded	18,012	17,170
Total loans individually evaluated for impairment	18,185	17,170
Loans collectively evaluated for impairment	399,346	408,169
Total recorded investment	418,127	425,940
Impaired loans with an allowance recorded	173	0
Impaired loans with no allowance recorded	26,801	26,057
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	26,974	26,057
Loans collectively evaluated for impairment	399,346	408,169
Financing Receivable Unpaid Principal Balance	427,035	434,946
Impaired loans with an allowance recorded	173	0
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	173	0
Loans collectively evaluated for impairment	5,346	5,500
Total loans held for investment	5,519	5,500
Construction and land development [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	9,812	15,426
Total loans individually evaluated for impairment	9,812	15,426
Loans collectively evaluated for impairment	1,947,677	1,616,778
Total recorded investment	1,957,489	1,632,204
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	26,440	32,289
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	26,440	32,289
Loans collectively evaluated for impairment	1,947,677	1,616,778
Financing Receivable Unpaid Principal Balance	1,974,117	1,649,067
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	22,594	19,599
Total loans held for investment	22,594	19,599
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	375	121
Total loans individually evaluated for impairment	375	121
Loans collectively evaluated for impairment	50,130	48,665
Total recorded investment	50,505	48,786
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	10,950	10,695
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	10,950	10,695
Loans collectively evaluated for impairment	50,130	48,665
Financing Receivable Unpaid Principal Balance	61,080	59,360
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	0	0
Loans collectively evaluated for impairment	800	776
Total loans held for investment	800	776
Receivables Acquired with Deteriorated Credit Quality [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	110,791	115,755
Loans acquired with deteriorated credit quality	139,875	144,925
Impaired loans with an allowance recorded	829	1,631
Receivables Acquired with Deteriorated Credit Quality [Member] | Owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	7,740	9,569
Loans acquired with deteriorated credit quality	9,945	12,619
Impaired loans with an allowance recorded	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Non-owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	102,418	105,542
Loans acquired with deteriorated credit quality	124,803	128,440
Impaired loans with an allowance recorded	827	1,629
Receivables Acquired with Deteriorated Credit Quality [Member] | Commercial and industrial [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	37	43
Loans acquired with deteriorated credit quality	4,412	3,146
Impaired loans with an allowance recorded	2	2
Receivables Acquired with Deteriorated Credit Quality [Member] | Residential real estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	596	601
Loans acquired with deteriorated credit quality	715	720
Impaired loans with an allowance recorded	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Construction and land development [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Loans acquired with deteriorated credit quality	0	0
Impaired loans with an allowance recorded	0	0
Receivables Acquired with Deteriorated Credit Quality [Member] | Consumer [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Loans acquired with deteriorated credit quality	0	0
Impaired loans with an allowance recorded	$ 0	$ 0