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, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	$ 5,244	$ 986
Impaired loans with no allowance recorded	138,154	111,266
Total loans individually evaluated for impairment	143,398	112,252
Loans collectively evaluated for impairment	17,910,128	17,514,822
Impaired Financing Receivable, Recorded Investment	143,398	112,252
Total recorded investment	18,116,748	17,710,629
Impaired loans with an allowance recorded	6,117	1,845
Impaired loans with no allowance recorded	220,177	198,234
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	226,294	200,079
Loans collectively evaluated for impairment	17,910,128	17,514,822
Financing Receivable Unpaid Principal Balance	18,220,551	17,820,320
Impaired loans with an allowance recorded	1,357	681
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	1,357	681
Loans collectively evaluated for impairment	153,521	151,940
Total loans held for investment	154,987	152,717
Owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	8,185	6,530
Total loans individually evaluated for impairment	8,185	6,530
Loans collectively evaluated for impairment	2,273,235	2,314,871
Total recorded investment	2,285,340	2,325,380
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	13,479	11,852
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	13,479	11,852
Loans collectively evaluated for impairment	2,273,235	2,314,871
Financing Receivable Unpaid Principal Balance	2,291,971	2,332,038
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	14,746	14,286
Total loans held for investment	14,746	14,286
Non-owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	12,268	12,407
Total loans individually evaluated for impairment	12,268	12,407
Loans collectively evaluated for impairment	4,232,710	4,121,464
Total recorded investment	4,304,261	4,213,428
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	14,398	18,155
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	14,398	18,155
Loans collectively evaluated for impairment	4,232,710	4,121,464
Financing Receivable Unpaid Principal Balance	4,321,561	4,235,299
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	23,020	20,456
Total loans held for investment	23,121	20,543
Commercial and industrial [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	590	623
Impaired loans with no allowance recorded	78,178	63,273
Total loans individually evaluated for impairment	78,768	63,896
Loans collectively evaluated for impairment	7,644,927	7,698,746
Total recorded investment	7,723,695	7,762,642
Impaired loans with an allowance recorded	1,463	1,482
Impaired loans with no allowance recorded	117,839	103,992
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	119,302	105,474
Loans collectively evaluated for impairment	7,644,927	7,698,746
Financing Receivable Unpaid Principal Balance	7,768,576	7,808,572
Impaired loans with an allowance recorded	297	621
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	297	621
Loans collectively evaluated for impairment	76,949	82,488
Total loans held for investment	77,254	83,118
Residential real estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	1,347	363
Impaired loans with no allowance recorded	14,070	19,381
Total loans individually evaluated for impairment	15,417	19,744
Loans collectively evaluated for impairment	1,446,125	1,184,592
Total recorded investment	1,461,561	1,204,355
Impaired loans with an allowance recorded	1,347	363
Impaired loans with no allowance recorded	22,428	27,979
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	23,775	28,342
Loans collectively evaluated for impairment	1,446,125	1,184,592
Financing Receivable Unpaid Principal Balance	1,469,972	1,213,006
Impaired loans with an allowance recorded	250	60
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	250	60
Loans collectively evaluated for impairment	12,756	11,216
Total loans held for investment	13,006	11,276
Construction and land development [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	3,307	0
Impaired loans with no allowance recorded	25,308	9,403
Total loans individually evaluated for impairment	28,615	9,403
Loans collectively evaluated for impairment	2,254,912	2,125,350
Total recorded investment	2,283,527	2,134,753
Impaired loans with an allowance recorded	3,307	0
Impaired loans with no allowance recorded	41,528	25,624
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	44,835	25,624
Loans collectively evaluated for impairment	2,254,912	2,125,350
Financing Receivable Unpaid Principal Balance	2,299,747	2,150,974
Impaired loans with an allowance recorded	810	0
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	810	0
Loans collectively evaluated for impairment	25,273	22,513
Total loans held for investment	26,083	22,513
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	145	272
Total loans individually evaluated for impairment	145	272
Loans collectively evaluated for impairment	58,219	69,799
Total recorded investment	58,364	70,071
Impaired loans with an allowance recorded	0	0
Impaired loans with no allowance recorded	10,505	10,632
Impaired Financing Receivable Unpaid Principal Balance Individually Evaluated For Impairment	10,505	10,632
Loans collectively evaluated for impairment	58,219	69,799
Financing Receivable Unpaid Principal Balance	68,724	80,431
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	777	981
Total loans held for investment	777	981
Financial Asset Acquired with Credit Deterioration [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	63,222	83,555
Loans acquired with deteriorated credit quality	84,129	105,419
Impaired loans with an allowance recorded	109	96
Financial Asset Acquired with Credit Deterioration [Member] | Owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	3,920	3,979
Loans acquired with deteriorated credit quality	5,257	5,315
Impaired loans with an allowance recorded	0	0
Financial Asset Acquired with Credit Deterioration [Member] | Non-owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	59,283	79,557
Loans acquired with deteriorated credit quality	74,453	95,680
Impaired loans with an allowance recorded	101	87
Financial Asset Acquired with Credit Deterioration [Member] | Commercial and industrial [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	0	0
Loans acquired with deteriorated credit quality	4,347	4,352
Impaired loans with an allowance recorded	8	9
Financial Asset Acquired with Credit Deterioration [Member] | Residential real estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired Financing Receivable, Recorded Investment	19	19
Loans acquired with deteriorated credit quality	72	72
Impaired loans with an allowance recorded	0	0
Financial Asset Acquired with Credit Deterioration [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
Financial Asset Acquired with Credit Deterioration [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