Derivative Financial Instruments - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) counterparty	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) counterparty	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Notional amount	$ 6,392,016		$ 6,392,016		$ 3,663,084
Net unrealized losses on interest rate agreements accounted for as cash flow hedges	$ 39,000		$ 39,000		$ 46,000
Number of counterparties | counterparty	7		7
Cash Flow Hedging | Interest rate swaps
Derivative [Line Items]
Notional amount	$ 139,500		$ 139,500
Valuation adjustments on derivatives	15,000	$ (5,000)	7,000	$ (14,000)
Loan Purchase and Forward Sales Commitments
Derivative [Line Items]
Valuation adjustments on derivatives	1,000		19,000
Unsecuritized Residential and Commercial Loans
Derivative [Line Items]
Valuation adjustments on derivatives	(17,000)	(12,000)		(25,000)
Unsecuritized Residential and Commercial Loans | Interest Rate Contract
Derivative [Line Items]
Notional amount	1,900,000		1,900,000
Unsecuritized Residential and Commercial Loans | Futures
Derivative [Line Items]
Notional amount	54,000		54,000
Unsecuritized Residential and Commercial Loans | TBAs
Derivative [Line Items]
Notional amount	2,500,000		2,500,000
Maximum
Derivative [Line Items]
Hedges decreased in value recorded as a component of interest expense (less than)	100	$ 100	100	$ 100
Maximum | Interest rate swaps
Derivative [Line Items]
Accumulated other comprehensive loss that will be amortized into interest expense (less than)	$ (1,000)		(1,000)
Maximum | Unsecuritized Residential and Commercial Loans
Derivative [Line Items]
Valuation adjustments on derivatives			$ (29,000)