Loans, Leases and Allowance for Credit Losses - Summary of Impairment Method Information Related to Loans and Allowance for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded (1)	$ 124,928	$ 25,754
Impaired loans with no allowance recorded	41,822	152,623
Total loans individually evaluated for impairment	166,750	178,377
Loans collectively evaluated for impairment	8,147,571	6,513,981
Loans acquired with deteriorated credit quality	96,474	118,323
Total recorded investment	8,410,795	6,810,681
Impaired loans with an allowance recorded	134,791	27,458
Impaired loans with no allowance recorded	44,220	170,302
Total loans individually evaluated for impairment	179,011	197,760
Loans collectively evaluated for impairment	8,147,571	6,513,981
Loans acquired with deteriorated credit quality	137,797	171,165
Total unpaid principal balance	8,464,379	6,882,906
Impaired loans with an allowance recorded	10,765	5,280
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	10,765	5,280
Loans collectively evaluated for impairment	99,188	94,448
Loans acquired with deteriorated credit quality	263	322
Total loans held for investment	110,216	100,050
Owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded (1)	28,024	1,092
Impaired loans with no allowance recorded	16,869	36,810
Total loans individually evaluated for impairment	44,893	37,902
Loans collectively evaluated for impairment	1,671,812	1,500,740
Loans acquired with deteriorated credit quality	17,912	23,220
Total recorded investment	1,734,617	1,561,862
Impaired loans with an allowance recorded	31,292	1,092
Impaired loans with no allowance recorded	17,010	43,537
Total loans individually evaluated for impairment	48,302	44,629
Loans collectively evaluated for impairment	1,671,812	1,500,740
Loans acquired with deteriorated credit quality	24,273	34,951
Total unpaid principal balance	1,744,387	1,580,320
Impaired loans with an allowance recorded	2,082	402
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	2,082	402
Loans collectively evaluated for impairment	10,198	12,158
Loans acquired with deteriorated credit quality	174	0
Total loans held for investment	12,454	12,560
Non-owner occupied [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded (1)	44,937	17,932
Impaired loans with no allowance recorded	21,387	55,220
Total loans individually evaluated for impairment	66,324	73,152
Loans collectively evaluated for impairment	1,916,474	1,678,242
Loans acquired with deteriorated credit quality	75,822	92,021
Total recorded investment	2,058,620	1,843,415
Impaired loans with an allowance recorded	45,853	19,273
Impaired loans with no allowance recorded	21,550	58,322
Total loans individually evaluated for impairment	67,403	77,595
Loans collectively evaluated for impairment	1,916,474	1,678,242
Loans acquired with deteriorated credit quality	108,935	130,279
Total unpaid principal balance	2,092,812	1,886,116
Impaired loans with an allowance recorded	2,537	2,121
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	2,537	2,121
Loans collectively evaluated for impairment	13,734	17,061
Loans acquired with deteriorated credit quality	58	322
Total loans held for investment	16,329	19,504
Commercial and industrial [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded (1)	11,399	1,907
Impaired loans with no allowance recorded	2,350	14,985
Total loans individually evaluated for impairment	13,749	16,892
Loans collectively evaluated for impairment	3,313,550	2,219,500
Loans acquired with deteriorated credit quality	330	348
Total recorded investment	3,327,629	2,236,740
Impaired loans with an allowance recorded	11,829	2,120
Impaired loans with no allowance recorded	4,104	15,731
Total loans individually evaluated for impairment	15,933	17,851
Loans collectively evaluated for impairment	3,313,550	2,219,500
Loans acquired with deteriorated credit quality	1,150	1,403
Total unpaid principal balance	3,330,633	2,238,754
Impaired loans with an allowance recorded	1,926	702
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	1,926	702
Loans collectively evaluated for impairment	49,809	36,344
Loans acquired with deteriorated credit quality	31	0
Total loans held for investment	51,766	37,046
Residential real estate [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded (1)	19,300	4,580
Impaired loans with no allowance recorded	0	21,796
Total loans individually evaluated for impairment	19,300	26,376
Loans collectively evaluated for impairment	277,162	321,683
Loans acquired with deteriorated credit quality	2,410	2,253
Total recorded investment	298,872	350,312
Impaired loans with an allowance recorded	24,420	4,729
Impaired loans with no allowance recorded	0	27,550
Total loans individually evaluated for impairment	24,420	32,279
Loans collectively evaluated for impairment	277,162	321,683
Loans acquired with deteriorated credit quality	3,439	3,728
Total unpaid principal balance	305,021	357,690
Impaired loans with an allowance recorded	1,052	1,896
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	1,052	1,896
Loans collectively evaluated for impairment	6,404	9,744
Loans acquired with deteriorated credit quality	0	0
Total loans held for investment	7,456	11,640
Construction and land development [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded (1)	21,052	118
Impaired loans with no allowance recorded	696	22,951
Total loans individually evaluated for impairment	21,748	23,069
Loans collectively evaluated for impairment	732,406	513,681
Loans acquired with deteriorated credit quality	0	481
Total recorded investment	754,154	537,231
Impaired loans with an allowance recorded	21,169	118
Impaired loans with no allowance recorded	885	24,137
Total loans individually evaluated for impairment	22,054	24,255
Loans collectively evaluated for impairment	732,406	513,681
Loans acquired with deteriorated credit quality	0	804
Total unpaid principal balance	754,460	538,740
Impaired loans with an allowance recorded	3,112	85
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	3,112	85
Loans collectively evaluated for impairment	15,446	14,434
Loans acquired with deteriorated credit quality	0	0
Total loans held for investment	18,558	14,519
Commercial leases [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded (1)	41	99
Impaired loans with no allowance recorded	332	350
Total loans individually evaluated for impairment	373	449
Loans collectively evaluated for impairment	203,897	235,519
Loans acquired with deteriorated credit quality	0	0
Total recorded investment	204,270	235,968
Impaired loans with an allowance recorded	41	99
Impaired loans with no allowance recorded	483	502
Total loans individually evaluated for impairment	524	601
Loans collectively evaluated for impairment	203,897	235,519
Loans acquired with deteriorated credit quality	0	0
Total unpaid principal balance	204,421	236,120
Impaired loans with an allowance recorded	39	70
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	39	70
Loans collectively evaluated for impairment	2,761	2,541
Loans acquired with deteriorated credit quality	0	0
Total loans held for investment	2,800	2,611
Consumer [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with an allowance recorded (1)	175	26
Impaired loans with no allowance recorded	188	511
Total loans individually evaluated for impairment	363	537
Loans collectively evaluated for impairment	32,270	44,616
Loans acquired with deteriorated credit quality	0	0
Total recorded investment	32,633	45,153
Impaired loans with an allowance recorded	187	27
Impaired loans with no allowance recorded	188	523
Total loans individually evaluated for impairment	375	550
Loans collectively evaluated for impairment	32,270	44,616
Loans acquired with deteriorated credit quality	0	0
Total unpaid principal balance	32,645	45,166
Impaired loans with an allowance recorded	17	4
Impaired loans with no allowance recorded	0	0
Total loans individually evaluated for impairment	17	4
Loans collectively evaluated for impairment	836	2,166
Loans acquired with deteriorated credit quality	0	0
Total loans held for investment	$ 853	$ 2,170