Impairment Charges and Impairment of Joint Venture Investments - Impairment Charges on Consolidated Assets (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Investments Debt And Equity Securities [Abstract]
Land held for development	$ 0	$ 6,400,000	$ 0	$ 6,400,000
Undeveloped land	2,600,000	19,100,000	2,600,000	19,100,000
Assets marketed for sale	31,800,000	16,600,000	34,900,000	16,600,000
Total continuing operations	34,439,000	42,101,000	37,525,000	42,132,000
Sold assets or assets held for sale	500,000	38,100,000	5,100,000	55,500,000
Total discontinued operations	542,000	38,126,000	5,135,000	55,466,000
Joint venture investments	0	0	0	560,000
Total impairment charges	$ 34,900,000	$ 80,200,000	$ 42,600,000	$ 98,200,000