Commitments and Contingencies - Contractual Commitments - Land Pipeline (Detail) $ / a in Thousands, $ in Thousands, ft² in Millions	Oct. 28, 2016 USD ($) a item $ / a	Sep. 30, 2016 a	Sep. 30, 2016 ft²	Dec. 31, 2015 a
Loss Contingencies [Line Items]
Area of a real estate property		1,581	1.5	148.35
Subsequent Event [Member]
Loss Contingencies [Line Items]
Area of a real estate property | a	4,054
Anticipated sale proceeds | $	$ 98,467
Anticipated revenue per acre | $ / a	24,000
Construction and Other Commitment [Member] | Subsequent Event [Member]
Loss Contingencies [Line Items]
Number of purchase and sale agreements | item	8
Number of buyers | item	7
Percentage area of real estate property	39.00%
Commercial | Subsequent Event [Member]
Loss Contingencies [Line Items]
Area of a real estate property | a	4
Anticipated sale proceeds | $	$ 1,175
Anticipated revenue per acre | $ / a	294,000
Mixed-Use Retail | Subsequent Event [Member]
Loss Contingencies [Line Items]
Area of a real estate property | a	22
Anticipated sale proceeds | $	$ 5,574
Anticipated revenue per acre | $ / a	253,000
Mixed-Use Retail | NADG | Subsequent Event [Member]
Loss Contingencies [Line Items]
Area of a real estate property | a	82
Anticipated sale proceeds | $	$ 20,187
Anticipated revenue per acre | $ / a	248,000
Commercial Tranche II | Subsequent Event [Member]
Loss Contingencies [Line Items]
Area of a real estate property | a	6
Anticipated sale proceeds | $	$ 1,470
Anticipated revenue per acre | $ / a	245,000
Age-restricted Residential | Minto Communities | Subsequent Event [Member]
Loss Contingencies [Line Items]
Area of a real estate property | a	1,581
Anticipated sale proceeds | $	$ 28,651
Anticipated revenue per acre | $ / a	18,000
AR Residential, Tranche II | Minto Communities | Subsequent Event [Member]
Loss Contingencies [Line Items]
Area of a real estate property | a	1,686
Anticipated sale proceeds | $	$ 31,360
Anticipated revenue per acre | $ / a	19,000
Single-tenant | Subsequent Event [Member]
Loss Contingencies [Line Items]
Area of a real estate property | a	73
Anticipated sale proceeds | $	$ 1,050
Anticipated revenue per acre | $ / a	14,000
Single-tenant | ICI | Subsequent Event [Member]
Loss Contingencies [Line Items]
Area of a real estate property | a	600
Anticipated sale proceeds | $	$ 9,000
Anticipated revenue per acre | $ / a	15,000