Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Unsecured Debt	$ 200,000,000	$ 200,000,000
Amount to be reclassified from accumulated other comprehensive loss to interest expense	1,800,000
Term Loans
Derivative [Line Items]
Notional amount of swap to hedge the variable cash flows associated with term loan	200,000,000
LIBOR Swap Agreement, period	3 years
Swap, fixed interest rate	1.11%
Spread over LIBOR	1.95%
Actual interest rate	3.06%
Accrued Liabilities [Member]
Derivative [Line Items]
Interest Rate Derivative Liabilities, at Fair Value	$ 3,013,000	$ 2,547,000