Aggregate Contractual Maturities of Indebtedness by Year (Parenthetical) (Detail) - USD ($) $ in Thousands		Mar. 31, 2018		Dec. 31, 2017
Extinguishment Of Debt [Line Items]
Unpaid Principal Balance		$ 1,298,211		$ 1,419,653
Recourse Indebtedness
Extinguishment Of Debt [Line Items]
Unpaid Principal Balance		283,387		313,700
Recourse Indebtedness | 7.0% convertible senior notes
Extinguishment Of Debt [Line Items]
Unpaid Principal Balance	[1]	$ 871		$ 871
Convertible senior notes interest rate		7.00%		7.00%
Recourse Indebtedness | 4.0% convertible senior notes
Extinguishment Of Debt [Line Items]
Unpaid Principal Balance		$ 104,513	[2]	$ 110,513	[3]
Convertible senior notes interest rate		4.00%		4.00%

[1] Our 7.0% convertible senior notes are redeemable at par, at the option of the holder, in April 2021, and April 2026.

[2] Our 4.0% convertible senior notes are redeemable at par, at the option of the holder, in October 2018, October 2023, and October 2028

[3] Our 4.0% convertible senior notes are redeemable at par, at the option of the holder, in October 2018, October 2023, and October 2028.