Unconsolidated Investments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Equity Method Investments and Joint Ventures [Abstract]
Amortization of basis difference for equity method investment	$ 2.8	$ 1.3	$ 5.6	$ 2.5
Gains on distributions from unconsolidated investments	$ 7.5			9.2
Distribution received in excess of carrying amount of the unconsolidated investments recorded within the memo ledger balance				9.2
Unrecorded Equity Earnings Or Losses				1.9
Unrecorded Other Comprehensive Income Or Loss For Suspended Equity-Method Investments				$ 0.1