Derivatives - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Notional amount of interest rate derivatives	$ 550,000,000	$ 290,000,000
Variable rate term loan agreement maturity	June 2013
Derivative, net hedge ineffectiveness gain (loss)	0
Amount reclassified to decrease to interest expense	300,000
Aggregate notional amount of mortgage banking derivatives	173,000,000	110,000,000
Termination value of derivatives in a net liability position	18,500,000
Collateral obligations for derivative counterparties	16,800,000
Interest rate swap [Member]
Derivative [Line Items]
Notional amount of interest rate derivatives	$ 140,000,000	$ 140,000,000