Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Total Assets	$ 27,933,375	$ 34,415,919
Total Liabilities	14,408,566	20,692,828
Non-Controlling Interests	3,333,954	$ 3,253,148
Cumulative-Effect Adjustment, Deconsolidation of Variable Interest Entity [Member]
Variable Interest Entity [Line Items]
Total Assets	(8,900,000)
Total Liabilities	(8,700,000)
Non-Controlling Interests	$ (196,100)