Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Company Lenders	Jun. 30, 2012	Dec. 31, 2012
Fair Value Measurements Of Financial Instruments [Line Items]
Interest and dividends	$ 629,000	$ 125,000	$ 668,000	$ 275,000
Mark-to-market gain (loss)	1,000,000	2,100,000	586,000	1,900,000
Allowance for uncollectible receivables	2,500,000		2,500,000		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	7,900,000		7,900,000
Surface Property
Fair Value Measurements Of Financial Instruments [Line Items]
Impairment of Long-Lived Assets Held-for-use			$ 741,000