Impairment Charges, Impairment of Joint Venture Investments and Reserves - Impairment Charges on Assets or Investments (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Impairment Charges And Impairment Of Joint Venture Investments [Abstract]
Assets marketed for sale		$ 325,400	$ 110,900	$ 179,700
Total continuing operations	$ 280,100	340,480	110,906	279,021
Reserve of preferred equity interests		61,000	0	0
Impairment of joint venture investments		0	0	1,909
Total impairment charges		401,500	110,900	280,900
Undeveloped Land [Member]
Impairment Charges And Impairment Of Joint Venture Investments [Abstract]
Undeveloped land previously held for development		$ 15,100	$ 0	$ 99,300