Derivatives - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Notional amount of interest rate derivatives	$ 752,936,000	$ 720,868,000
Variable rate term loan agreement maturity	June 2013.
Derivative, net hedge ineffectiveness gain (loss)	0	0
Termination value of derivatives in a net liability position	10,100,000
Collateral obligations for derivative counterparties	11,100,000
Interest rate swap [Member]
Derivative [Line Items]
Notional amount of interest rate derivatives	$ 140,000,000