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	Mar. 31, 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	$ 3,069,316	$ 3,042,842
Commercial Real Estate Credit Exposure [Member] | Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	2,800,505	2,762,372
Commercial Real Estate Credit Exposure [Member] | Pass-Watch [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	69,484	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	33,524	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	164,818	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	985	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	2,110,096	2,022,529
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	1,953,908	1,864,116
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	52,052	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	18,944	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	85,178	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	14	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	907,170	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	839,044	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	9,606	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	13,412	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	45,108	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	52,050	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	7,553	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	7,826	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	1,168	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	34,532	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	971	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	1,720,307	1,720,614
Residential mortgages [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,228,170	1,196,256
Residential mortgages [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	293,111	315,340
Residential mortgages [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	199,026	209,018
Residential mortgages [Member] | Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,696,782	1,698,359
Residential mortgages [Member] | Performing [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	1,212,619	1,182,266
Residential mortgages [Member] | Performing [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	285,140	307,078
Residential mortgages [Member] | Performing [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	199,023	209,015
Residential mortgages [Member] | Nonperforming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	23,525	22,255
Residential mortgages [Member] | Nonperforming [Member] | Originated loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	15,551	13,990
Residential mortgages [Member] | Nonperforming [Member] | Acquired loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	7,971	8,262
Residential mortgages [Member] | Nonperforming [Member] | Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit risk profile by internally assigned grade	$ 3	$ 3