Summarized Statements of Operations for Unconsolidated Investments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Investments in and Advances to Affiliates [Line Items]
Total revenues	$ 22,614	$ 55,907	$ 30,357	$ 30,518	$ 19,820	$ 26,745	$ 25,284	$ 73,436	$ 139,396	$ 145,285	$ 99,540
Total expenses									137,262	532,092	151,094
Net income (loss)									5,990	(330,308)	(35,905)
Statements Of Operations
Investments in and Advances to Affiliates [Line Items]
Total revenues									82	11	14
Total expenses									1,124	1,042	2,847
Net income (loss)									$ (1,042)	$ (1,031)	$ (2,833)