Impairment Charges, Impairment of Joint Venture Investments and Reserves - Summary of Significant Unobservable Inputs (Detail) - Fair Value Measurements [Member] $ / ft² in Thousands, $ / a in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / a	Dec. 31, 2016 USD ($) $ / ft²	Dec. 31, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 1,556.1	$ 438.2	$ 407.1
Fair Value	272.0
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	1,556.1	438.2	$ 407.1
Fair Value	272.0
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Indicative Bid/Contracted Price [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	166.8	13.4
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Income Capitalization/Sales Comparison Approach [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 882.6	$ 398.2
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Income Capitalization/Sales Comparison Approach [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Price per Square Foot, Range | $ / ft²		15
Range	6.25%	7.00%
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Income Capitalization/Sales Comparison Approach [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Price per Square Foot, Range | $ / ft²		31
Range	10.00%	10.00%
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Indicative Bid [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		$ 26.6
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 499.3
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	7.75%	10.00%
Range	7.45%	10.00%
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	9.50%	11.00%
Range	21.39%	12.00%
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Sales Comparison Approach [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 7.4
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Sales Comparison Approach [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Price per Acre, Range | $ / a	50
Impairment of Consolidated Assets [Member] | Level 3 [Member] | Sales Comparison Approach [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Price per Acre, Range | $ / a	218
Reserve of Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 272.0
Range	1.00%
Reserve of Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	8.40%
Range	7.80%
Reserve of Preferred Equity Interests [Member] | Level 3 [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	8.80%
Range	8.50%