Loans and Allowance for Loan Losses - Schedule of Credit Quality Indicators of Various Classes of Loans - Credit Risk Profile by Internally Assigned Grade (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Commercial Real Estate Credit Exposure [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	$ 3,100,834	$ 3,042,841
Commercial Real Estate Credit Exposure [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,813,783	2,762,371
Commercial Real Estate Credit Exposure [Member] | Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	98,265	69,374
Commercial Real Estate Credit Exposure [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	35,734	37,582
Commercial Real Estate Credit Exposure [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	152,991	165,626
Commercial Real Estate Credit Exposure [Member] | Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	61	7,888
Commercial Real Estate Credit Exposure [Member] | Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Real Estate Credit Exposure [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,245,855	2,022,528
Commercial Real Estate Credit Exposure [Member] | Originated Loans [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,048,886	1,864,115
Commercial Real Estate Credit Exposure [Member] | Originated Loans [Member] | Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	83,729	49,578
Commercial Real Estate Credit Exposure [Member] | Originated Loans [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	25,842	15,785
Commercial Real Estate Credit Exposure [Member] | Originated Loans [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	87,369	93,034
Commercial Real Estate Credit Exposure [Member] | Originated Loans [Member] | Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	29	16
Commercial Real Estate Credit Exposure [Member] | Originated Loans [Member] | Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Real Estate Credit Exposure [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	813,429	967,148
Commercial Real Estate Credit Exposure [Member] | Acquired Loans [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	758,092	896,578
Commercial Real Estate Credit Exposure [Member] | Acquired Loans [Member] | Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	8,725	9,530
Commercial Real Estate Credit Exposure [Member] | Acquired Loans [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	9,029	19,798
Commercial Real Estate Credit Exposure [Member] | Acquired Loans [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	37,583	41,242
Commercial Real Estate Credit Exposure [Member] | Acquired Loans [Member] | Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Real Estate Credit Exposure [Member] | Acquired Loans [Member] | Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Commercial Real Estate Credit Exposure [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	41,550	53,165
Commercial Real Estate Credit Exposure [Member] | Covered Loans [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	6,805	1,678
Commercial Real Estate Credit Exposure [Member] | Covered Loans [Member] | Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	5,811	10,266
Commercial Real Estate Credit Exposure [Member] | Covered Loans [Member] | Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	863	1,999
Commercial Real Estate Credit Exposure [Member] | Covered Loans [Member] | Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	28,039	31,350
Commercial Real Estate Credit Exposure [Member] | Covered Loans [Member] | Doubtful [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	32	7,872
Commercial Real Estate Credit Exposure [Member] | Covered Loans [Member] | Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,858,490	1,720,614
Residential Mortgages [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,847,759	1,698,359
Residential Mortgages [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	10,731	22,255
Residential Mortgages [Member] | Originated Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,635,462	1,196,256
Residential Mortgages [Member] | Originated Loans [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,624,959	1,182,266
Residential Mortgages [Member] | Originated Loans [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	10,503	13,990
Residential Mortgages [Member] | Acquired Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	37,739	315,340
Residential Mortgages [Member] | Acquired Loans [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	37,511	307,078
Residential Mortgages [Member] | Acquired Loans [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	228	8,262
Residential Mortgages [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	185,289	209,018
Residential Mortgages [Member] | Covered Loans [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	185,289	209,015
Residential Mortgages [Member] | Covered Loans [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade		$ 3