Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013 Company Lenders	Mar. 31, 2012	Dec. 31, 2012
Fair Value Measurements Of Financial Instruments [Line Items]
Interest and dividends	$ 40,000	$ 62,000
Mark-to-market gain (loss)	1,600,000	4,000,000
Allowance for uncollectible receivables	2,400,000		2,400,000
Number of financial institutions included in counter parties	15
Number of secured lenders not in banking credit facility	2
Net derivative asset	$ 3,400,000