Loans - Schedule of Aging of Non-Covered Loans (Detail) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2015		Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable
Discount (premium)		$ 26,300		$ 20,600
Non-covered loans, net of unearned income		$ 13,863,478		10,996,500
Past due loans threshold period		90 days
Non-Covered Legacy Loans
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[1]	$ 9,450		23,365
Past due, 60-89 days	[1]	6,267		6,202
Past due, greater than 90 days	[1]	52,795		35,724
Total past due	[1]	68,512		65,291
Current		10,710,746		9,603,423
Non-covered loans, net of unearned income		10,779,258		9,668,714
Recorded investment greater than 90 days and accruing		1,521		754
Non-Covered Legacy Loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans, net of unearned income		7,815,161		7,002,198
Non-Covered Legacy Loans | Commercial Loans | Commercial Real Estate - Construction
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[1]	0		507
Past due, 60-89 days	[1]	0		0
Past due, greater than 90 days	[1]	180		69
Total past due	[1]	180		576
Current		559,028		483,663
Non-covered loans, net of unearned income		559,208		484,239
Recorded investment greater than 90 days and accruing		0		0
Non-Covered Legacy Loans | Commercial Loans | Commercial Real Estate - Other
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[1]	1,225		11,799
Past due, 60-89 days	[1]	1,763		148
Past due, greater than 90 days	[1]	14,541		6,859
Total past due	[1]	17,529		18,806
Current		3,744,986		3,173,766
Non-covered loans, net of unearned income		3,762,515		3,192,572
Recorded investment greater than 90 days and accruing		242		0
Non-Covered Legacy Loans | Commercial Loans | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[1]	1,087		1,589
Past due, 60-89 days	[1]	672		1,860
Past due, greater than 90 days	[1]	11,139		3,225
Total past due	[1]	12,898		6,674
Current		2,766,605		2,445,847
Non-covered loans, net of unearned income		2,779,503		2,452,521
Recorded investment greater than 90 days and accruing		363		200
Non-Covered Legacy Loans | Commercial Loans | Energy-Related
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[1]	0		0
Past due, 60-89 days	[1]	0		0
Past due, greater than 90 days	[1]	3,478		27
Total past due	[1]	3,478		27
Current		710,457		872,839
Non-covered loans, net of unearned income		713,935		872,866
Recorded investment greater than 90 days and accruing		0		0
Non-Covered Legacy Loans | Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans, net of unearned income		660,543		527,694
Non-Covered Legacy Loans | Residential Mortgage Loans | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[1]	1,832		1,389
Past due, 60-89 days	[1]	2,054		2,616
Past due, greater than 90 days	[1]	15,730		14,900
Total past due	[1]	19,616		18,905
Current		640,927		508,789
Non-covered loans, net of unearned income		660,543		527,694
Recorded investment greater than 90 days and accruing		851		538
Non-Covered Legacy Loans | Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans, net of unearned income		2,303,554		2,138,822
Non-Covered Legacy Loans | Consumer and Other Loans | Consumer - Home Equity
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[1]	2,232		4,096
Past due, 60-89 days	[1]	853		595
Past due, greater than 90 days	[1]	5,343		7,420
Total past due	[1]	8,428		12,111
Current		1,480,368		1,278,865
Non-covered loans, net of unearned income		1,488,796		1,290,976
Recorded investment greater than 90 days and accruing		65		16
Non-Covered Legacy Loans | Consumer and Other Loans | Consumer - Indirect Automobile
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[1]	1,927		2,447
Past due, 60-89 days	[1]	470		396
Past due, greater than 90 days	[1]	1,129		1,419
Total past due	[1]	3,526		4,262
Current		277,996		392,504
Non-covered loans, net of unearned income		281,522		396,766
Recorded investment greater than 90 days and accruing		0		0
Non-Covered Legacy Loans | Consumer and Other Loans | Consumer - Credit Card
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[1]	247		253
Past due, 60-89 days	[1]	116		163
Past due, greater than 90 days	[1]	335		1,032
Total past due	[1]	698		1,448
Current		76,018		71,297
Non-covered loans, net of unearned income		76,716		72,745
Recorded investment greater than 90 days and accruing		0		0
Non-Covered Legacy Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[1]	900		1,285
Past due, 60-89 days	[1]	339		424
Past due, greater than 90 days	[1]	920		773
Total past due	[1]	2,159		2,482
Current		454,361		375,853
Non-covered loans, net of unearned income		456,520		378,335
Recorded investment greater than 90 days and accruing		0		0
Non-Covered Acquired Loans
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days		6,567	[2]	11,537
Past due, 60-89 days		2,201	[2]	3,849
Past due, greater than 90 days		67,361	[2]	49,470
Total past due		76,129	[2]	64,856
Current		3,073,002		1,326,950
Discount (premium)		(64,911)		(64,020)
Non-covered loans, net of unearned income		3,084,220		1,327,786
Recorded investment greater than 90 days and accruing		63,972		47,603
Non-Covered Acquired Loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans, net of unearned income		2,132,008		591,498
Non-Covered Acquired Loans | Commercial Loans | Commercial Real Estate - Construction
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[2]	0		2,740
Past due, 60-89 days	[2]	260		57
Past due, greater than 90 days	[2]	6,965		1,284
Total past due	[2]	7,225		4,081
Current		118,084		26,667
Discount (premium)		(1,548)		(1,170)
Non-covered loans, net of unearned income		123,761		29,578
Recorded investment greater than 90 days and accruing		6,965		1,284
Non-Covered Acquired Loans | Commercial Loans | Commercial Real Estate - Other
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[2]	3,267		4,419
Past due, 60-89 days	[2]	25		840
Past due, greater than 90 days	[2]	40,206		26,480
Total past due	[2]	43,498		31,739
Current		1,487,123		473,644
Discount (premium)		(39,944)		(39,119)
Non-covered loans, net of unearned income		1,490,677		466,264
Recorded investment greater than 90 days and accruing		39,066		26,376
Non-Covered Acquired Loans | Commercial Loans | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[2]	1,464		2,106
Past due, 60-89 days	[2]	346		70
Past due, greater than 90 days	[2]	6,566		1,624
Total past due	[2]	8,376		3,800
Current		508,047		89,338
Discount (premium)		(4,374)		(5,224)
Non-covered loans, net of unearned income		512,049		87,914
Recorded investment greater than 90 days and accruing		5,882		1,635
Non-Covered Acquired Loans | Commercial Loans | Energy-Related
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[2]	95		0
Past due, 60-89 days	[2]	382		0
Past due, greater than 90 days	[2]	1,392		11
Total past due	[2]	1,869		11
Current		3,652		7,731
Discount (premium)		0		0
Non-covered loans, net of unearned income		5,521		7,742
Recorded investment greater than 90 days and accruing		1,392		0
Non-Covered Acquired Loans | Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans, net of unearned income		409,472		424,579
Non-Covered Acquired Loans | Residential Mortgage Loans | Residential Mortgage
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[2]	85		152
Past due, 60-89 days	[2]	846		2,367
Past due, greater than 90 days	[2]	5,470		9,339
Total past due	[2]	6,401		11,858
Current		407,673		418,552
Discount (premium)		(4,602)		(5,831)
Non-covered loans, net of unearned income		409,472		424,579
Recorded investment greater than 90 days and accruing		4,430		8,087
Non-Covered Acquired Loans | Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Non-covered loans, net of unearned income		542,740		311,709
Non-Covered Acquired Loans | Consumer and Other Loans | Consumer - Home Equity
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[2]	1,063		649
Past due, 60-89 days	[2]	221		385
Past due, greater than 90 days	[2]	6,097		8,774
Total past due	[2]	7,381		9,808
Current		452,928		216,310
Discount (premium)		(10,644)		(8,419)
Non-covered loans, net of unearned income		449,665		217,699
Recorded investment greater than 90 days and accruing		5,643		8,383
Non-Covered Acquired Loans | Consumer and Other Loans | Consumer - Indirect Automobile
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[2]	0		13
Past due, 60-89 days	[2]	5		17
Past due, greater than 90 days	[2]	19		9
Total past due	[2]	24		39
Current		142		393
Discount (premium)		(39)		(40)
Non-covered loans, net of unearned income		127		392
Recorded investment greater than 90 days and accruing		19		9
Non-Covered Acquired Loans | Consumer and Other Loans | Consumer - Other
Accounts, Notes, Loans and Financing Receivable
Past due, 30-59 days	[2]	593		1,458
Past due, 60-89 days	[2]	116		113
Past due, greater than 90 days	[2]	646		1,949
Total past due	[2]	1,355		3,520
Current		95,353		94,315
Discount (premium)		(3,760)		(4,217)
Non-covered loans, net of unearned income		92,948		93,618
Recorded investment greater than 90 days and accruing		$ 575		$ 1,829

[1] Past due loans greater than 90 days days include all loans on non-accrual status, regardless of past due status, as of the period indicated. Non-accrual loans are presented separately in the “Non-accrual Loans” section below.

[2] Past due information presents acquired loans at the gross loan balance, prior to application of discounts.