Senior Secured Notes and Subordinated Notes (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Fair Value	$ 5,830,973	$ 11,339,206
Senior Secured Notes
Debt Instrument [Line Items]
Borrowing Outstanding	3,542,077	3,514,815
Fair Value	5,615,419	10,595,652
Subordinated Notes
Debt Instrument [Line Items]
Fair Value	215,554	743,554
Non-Consolidated Affiliates Senior Secured Notes
Debt Instrument [Line Items]
Borrowing Outstanding	114,909	54,400
Fair Value	68,603	41,386
Non-Consolidated Affiliates Senior Secured Notes | Senior Secured Notes
Debt Instrument [Line Items]
Borrowing Outstanding	3,250	1,000
Fair Value	3,269	996
Non-Consolidated Affiliates Senior Secured Notes | Subordinated Notes
Debt Instrument [Line Items]
Borrowing Outstanding	111,659	53,400
Fair Value	$ 65,334	$ 40,390