Derivatives - Additional Information (Detail) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
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	8,700,000
Collateral obligations for derivative counterparties	6,200,000
Interest rate swap [Member]
Derivative [Line Items]
Notional amount of interest rate derivatives	$ 140,000,000