Unconsolidated Investments - Summarized Operating Results of Unconsolidated Investees (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Schedule of Equity Method Investments [Line Items]
Revenue	$ 82,744	$ 54,147	$ 183,103	$ 126,563
Cost of revenue	28,149	23,618	57,738	46,045
Operating expenses	919	578	1,633	1,022
Other expense	15,135	30,177	37,976	68,267
Net income (loss)	38,541	(226)	85,756	11,229
South Kent [Member]
Schedule of Equity Method Investments [Line Items]
Revenue	26,727	21,376	58,881	49,905
Cost of revenue	7,480	8,389	15,931	16,385
Operating expenses	278	239	467	427
Other expense	(170)	13,268	5,973	32,957
Net income (loss)	$ 19,139	$ (520)	$ 36,510	$ 136