Stockholders' Equity - Summary of Noncontrolling Interest Balances (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance			$ 1,253,693	$ 891,246
Acquisitions			52,493	390,389
Sale of subsidiaries			(32,278)
Distributions to noncontrolling interests			(28,867)	(13,701)
Other				(201)
Net loss	$ (18,952)	$ (18,548)	(201,986)	(50,566)
Other comprehensive income, net of tax			2,296	182
Ending balance	1,045,351	1,217,349	1,045,351	1,217,349
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			52,493	390,389
Sale of subsidiaries			(36,910)
Distributions to noncontrolling interests			(28,867)	(13,701)
Other				(201)
Net loss			0	0
Other comprehensive income, net of tax			0	0
Ending balance	1,367,056	1,330,729	1,367,056	1,330,729
Accumulated Income (Loss) [Member]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance			(127,119)	(62,614)
Acquisitions			0	0
Sale of subsidiaries			4,632
Distributions to noncontrolling interests			0	0
Other				0
Net loss			(201,986)	(50,566)
Other comprehensive income, net of tax			0	0
Ending balance	(324,473)	(113,180)	(324,473)	(113,180)
Accumulated Other Comprehensive Income [Member]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning balance			472	(382)
Acquisitions			0	0
Sale of subsidiaries			0
Distributions to noncontrolling interests			0	0
Other				0
Net loss			0	0
Other comprehensive income, net of tax			2,296	182
Ending balance	$ 2,768	$ (200)	$ 2,768	$ (200)