Loans and Allowance for Loan Losses - Schedule of Credit Quality Indicators of Various Classes of Loans - Credit Risk Profile Based on Payment Activity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Commercial Non Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	$ 5,587,137	$ 5,064,224
Commercial Non Real Estate Credit Exposure [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	4,806,740	4,113,837
Commercial Non Real Estate Credit Exposure [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	769,226	926,997
Commercial Non Real Estate Credit Exposure [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	11,171	23,390
Commercial Non Real Estate Credit Exposure [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	5,356,866	4,846,931
Commercial Non Real Estate Credit Exposure [Member] | Pass [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	4,656,899	3,990,320
Commercial Non Real Estate Credit Exposure [Member] | Pass [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	698,111	846,134
Commercial Non Real Estate Credit Exposure [Member] | Pass [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,856	10,477
Commercial Non Real Estate Credit Exposure [Member] | Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	91,266	90,848
Commercial Non Real Estate Credit Exposure [Member] | Pass-Watch [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	58,894	46,734
Commercial Non Real Estate Credit Exposure [Member] | Pass-Watch [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	32,372	44,105
Commercial Non Real Estate Credit Exposure [Member] | Pass-Watch [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity		9
Commercial Non Real Estate Credit Exposure [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	54,025	64,624
Commercial Non Real Estate Credit Exposure [Member] | Special Mention [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	26,869	41,812
Commercial Non Real Estate Credit Exposure [Member] | Special Mention [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	26,635	19,915
Commercial Non Real Estate Credit Exposure [Member] | Special Mention [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	521	2,897
Commercial Non Real Estate Credit Exposure [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	84,861	60,063
Commercial Non Real Estate Credit Exposure [Member] | Substandard [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	63,959	34,276
Commercial Non Real Estate Credit Exposure [Member] | Substandard [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	12,108	16,125
Commercial Non Real Estate Credit Exposure [Member] | Substandard [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	8,794	9,662
Commercial Non Real Estate Credit Exposure [Member] | Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	119	1,758
Commercial Non Real Estate Credit Exposure [Member] | Doubtful [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	119	695
Commercial Non Real Estate Credit Exposure [Member] | Doubtful [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity		718
Commercial Non Real Estate Credit Exposure [Member] | Doubtful [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity		345
Commercial Non Real Estate Credit Exposure [Member] | Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity
Commercial Non Real Estate Credit Exposure [Member] | Loss [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity
Commercial Non Real Estate Credit Exposure [Member] | Loss [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity
Commercial Non Real Estate Credit Exposure [Member] | Loss [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity
Construction Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,095,902	915,541
Construction Credit Exposure [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	974,442	752,381
Construction Credit Exposure [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	110,294	142,931
Construction Credit Exposure [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	11,166	20,229
Construction Credit Exposure [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,008,190	822,035
Construction Credit Exposure [Member] | Pass [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	923,800	709,261
Construction Credit Exposure [Member] | Pass [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	82,067	112,773
Construction Credit Exposure [Member] | Pass [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	2,323	1
Construction Credit Exposure [Member] | Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	21,487	10,950
Construction Credit Exposure [Member] | Pass-Watch [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	17,576	7,817
Construction Credit Exposure [Member] | Pass-Watch [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	2,911	1,907
Construction Credit Exposure [Member] | Pass-Watch [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,000	1,226
Construction Credit Exposure [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	11,598	13,611
Construction Credit Exposure [Member] | Special Mention [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	5,832	3,926
Construction Credit Exposure [Member] | Special Mention [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	5,737	9,409
Construction Credit Exposure [Member] | Special Mention [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	29	276
Construction Credit Exposure [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	54,627	61,717
Construction Credit Exposure [Member] | Substandard [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	27,234	31,377
Construction Credit Exposure [Member] | Substandard [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	19,579	18,842
Construction Credit Exposure [Member] | Substandard [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	7,814	11,498
Construction Credit Exposure [Member] | Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity		7,228
Construction Credit Exposure [Member] | Doubtful [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity
Construction Credit Exposure [Member] | Doubtful [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity
Construction Credit Exposure [Member] | Doubtful [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity		7,228
Construction Credit Exposure [Member] | Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity
Construction Credit Exposure [Member] | Loss [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity
Construction Credit Exposure [Member] | Loss [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity
Construction Credit Exposure [Member] | Loss [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,706,211	1,581,597
Consumer [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,623,069	1,409,130
Consumer [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	51,488	119,603
Consumer [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	31,654	52,864
Consumer [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,701,293	1,574,685
Consumer [Member] | Performing [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	1,618,779	1,404,032
Consumer [Member] | Performing [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	50,895	117,789
Consumer [Member] | Performing [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	31,619	52,864
Consumer [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	4,918	6,912
Consumer [Member] | Nonperforming [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	4,290	5,098
Consumer [Member] | Nonperforming [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	593	1,814
Consumer [Member] | Nonperforming [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile based on payment activity	$ 35