Quarterly Results of Operations - Summary of Quarterly Results of Operations (Parenthetical) (Detail) (USD $)	3 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Results Of Operations [Line Items]
Impairment charges	$ 20,600,000	$ 47,400,000	$ 153,142,000	$ 128,765,000	$ 172,127,000
Gain on sale of real estate	$ 400,000	$ 54,300,000