Stockholders' Equity - Summary of Noncontrolling Interest Balances (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance			$ 1,253,693	$ 891,246
Acquisitions			11,113
Contributions from noncontrolling interests				325,600
Distributions to noncontrolling interests			(21,274)	(9,164)
Other				(127)
Net loss	$ (34,492)	$ (28,904)	(183,034)	(32,018)
Other comprehensive loss, net of tax			(1,752)	(107)
Ending balance	1,058,746	1,175,430	1,058,746	1,175,430
Tax reform, change in tax rate	150,000
Capital [Member]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance			1,380,340	954,242
Acquisitions			11,113
Contributions from noncontrolling interests				325,600
Distributions to noncontrolling interests			(21,274)	(9,164)
Other				(127)
Net loss			0	0
Other comprehensive loss, net of tax			0	0
Ending balance	1,370,179	1,270,551	1,370,179	1,270,551
Accumulated Income (Loss) [Member]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance			(127,119)	(62,614)
Acquisitions			0
Contributions from noncontrolling interests				0
Distributions to noncontrolling interests			0	0
Other				0
Net loss			(183,034)	(32,018)
Other comprehensive loss, net of tax			0	0
Ending balance	(310,153)	(94,632)	(310,153)	(94,632)
Accumulated Other Comprehensive Income [Member]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance			472	(382)
Acquisitions			0
Contributions from noncontrolling interests				0
Distributions to noncontrolling interests			0	0
Other				0
Net loss			0	0
Other comprehensive loss, net of tax			(1,752)	(107)
Ending balance	$ (1,280)	$ (489)	$ (1,280)	$ (489)