Commitments and Contingencies - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2015 USD ($) Contract	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jun. 30, 2014 USD ($)	Sep. 30, 2013 USD ($)
Commitments And Contingencies [Line Items]
Net rental expense		$ 31,700,000	$ 21,200,000	$ 19,900,000
Net of rental income		3,800,000	3,100,000	3,300,000
Operating lease termination period	20 years
Gain recognized on lease termination				11,300,000
Aggregate fair value of net liability position		36,000,000
Collateral posted		$ 53,000,000
Subordinated Notes Due September 27, 2023 [Member]
Commitments And Contingencies [Line Items]
Debt instrument percentage		5.125%
Derivatives Designated as Hedging Instruments [Member]
Commitments And Contingencies [Line Items]
Notional amount of interest rate derivatives		$ 1,040,209,000	1,140,406,000
Derivatives Not Designated as Hedging Instrument [Member]
Commitments And Contingencies [Line Items]
Notional amount of interest rate derivatives		727,572,000	419,706,000
Interest Rate Swaps [Member]
Commitments And Contingencies [Line Items]
Accumulated net after-tax losses related to effective cash flow hedges		17,600,000	14,500,000
Estimated amount of interest rate derivatives to be reclassified to interest expense		11,800,000
Recognized a net reduction to interest expense			100,000	$ 584,000
Interest Rate Swaps [Member] | Derivatives Not Designated as Hedging Instrument [Member]
Commitments And Contingencies [Line Items]
Notional amount of interest rate derivatives		$ 654,134,000	378,849,000
Cash Flow Hedge [Member] | Forward-Settle Interest Rate Swap [Member]
Commitments And Contingencies [Line Items]
Notional amount of interest rate derivatives						$ 65,000,000
Cash Flow Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps Associated With Prime-Rate Indexed Deposits [Member]
Commitments And Contingencies [Line Items]
Number of derivative contracts held (in contract) | Contract		4
Notional amount of interest rate derivatives		$ 300,000,000
Cash Flow Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps Associated With Prime-Rate Indexed Deposits [Member] | Fixed Rate At Approximately Four Point Seven Three Percent [Member]
Commitments And Contingencies [Line Items]
Number of derivative contracts held (in contract) | Contract		2
Notional amount of derivative asset		$ 200,000,000
Derivative, Fixed Interest Rate		4.73%
Cash Flow Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps Associated With Prime-Rate Indexed Deposits [Member] | Fixed Rate At Approximately Five Point Eleven Percent [Member]
Commitments And Contingencies [Line Items]
Number of derivative contracts held (in contract) | Contract		2
Notional amount of interest rate derivatives		$ 100,000,000
Derivative, Fixed Interest Rate		5.11%
Cash Flow Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps Due September 27, 2023 [Member]
Commitments And Contingencies [Line Items]
Number of derivative contracts held (in contract) | Contract		1
Notional amount of derivative asset		$ 125,000,000
Derivative, Cap Interest Rate		7.44%
Cash Flow Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps Due Between November 2018 And November 2020 [Member]
Commitments And Contingencies [Line Items]
Number of derivative contracts held (in contract) | Contract		3
Notional amount of derivative asset		$ 300,000,000
Cash Flow Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps Due Between November 2018 And November 2020 [Member] | Minimum [Member]
Commitments And Contingencies [Line Items]
Derivative, Fixed Interest Rate		2.57%
Cash Flow Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps Due Between November 2018 And November 2020 [Member] | Maximum [Member]
Commitments And Contingencies [Line Items]
Derivative, Fixed Interest Rate		2.97%
Cash Flow Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps Due Between March 2019 And September 2020
Commitments And Contingencies [Line Items]
Number of derivative contracts held (in contract) | Contract		4
Notional amount of derivative asset		$ 182,000,000
Cash Flow Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps Due Between March 2019 And September 2020 | Minimum [Member]
Commitments And Contingencies [Line Items]
Derivative, Fixed Interest Rate		2.51%
Cash Flow Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps Due Between March 2019 And September 2020 | Maximum [Member]
Commitments And Contingencies [Line Items]
Derivative, Fixed Interest Rate		2.88%
Designated as Fair Value Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member]
Commitments And Contingencies [Line Items]
Notional amount of interest rate derivatives		$ 133,209,000	$ 133,406,000
Designated as Fair Value Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Consumer And Commercial Money Market Deposit Accounts [Member]
Commitments And Contingencies [Line Items]
Notional amount of interest rate derivatives		$ 8,200,000
Designated as Fair Value Hedge [Member] | Interest Rate Swaps [Member] | Derivatives Designated as Hedging Instruments [Member] | Market Linked Certificates Of Deposit [Member]
Commitments And Contingencies [Line Items]
Notional amount of interest rate derivatives					$ 25,000,000