Line items represent reporting concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Cost and Equity Method Investments - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Investment [Line Items]
Equity Income	$ 3,176,000
Equity method investments	104,718,000		$ 101,562,000
Cost method investments	13,580,000		6,005,000
Investments Carried Under Measurements Alternative [Member]
Investment [Line Items]
Gain or loss relating to cost method investments	$ 0	$ 0
Real Estate LP [Member]
Investment [Line Items]
Equity method investment ownership percentage	27.00%
Other Assets [Member]
Investment [Line Items]
Equity method investments	$ 104,700,000		101,600,000
Other Assets [Member] \| Investments Carried Under Measurements Alternative [Member]
Investment [Line Items]
Cost method investments	13,600,000		$ 6,000,000
Other Income, Net [Member]
Investment [Line Items]
Equity Income	$ 3,200,000