Fair Value Measurements - Derivative Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Liabilities
Common stock warrants	$ (6,808)	$ (5,134)
Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	26,274	29,887
Derivative asset, fair value, gross liability	(19,650)	(23,601)
Derivative asset	6,624	6,286
Liabilities
Fair value of derivative liability	(46,061)	(49,424)
Derivative liability, fair value, gross asset	19,650	23,601
Derivative liability	(26,411)	(25,823)
Cash collateral	7,200	9,700
Interest rate derivatives \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	3,810	3,602
Derivative asset, fair value, gross liability	0	(64)
Derivative asset	3,810	3,538
Liabilities
Fair value of derivative liability		(158)
Derivative liability, fair value, gross asset		64
Derivative liability		(94)
Fair Value, Inputs, Level 1 \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	557	190
Liabilities
Fair value of derivative liability	(596)	(54)
Fair Value, Inputs, Level 1 \| Interest rate derivatives \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	0	0
Liabilities
Fair value of derivative liability		0
Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	25,717	29,697
Liabilities
Fair value of derivative liability	(19,093)	(24,236)
Fair Value, Inputs, Level 2 \| Interest rate derivatives \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	3,810	3,602
Liabilities
Fair value of derivative liability		(158)
Fair Value, Inputs, Level 3 \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	0	0
Liabilities
Fair value of derivative liability	(26,372)	(25,134)
Fair Value, Inputs, Level 3 \| Interest rate derivatives \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	0	0
Liabilities
Fair value of derivative liability		0
Exchange Traded \| Future \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	22,464	26,285
Derivative asset, fair value, gross liability	(19,650)	(23,537)
Derivative asset	2,814	2,748
Liabilities
Fair value of derivative liability	(19,689)	(24,132)
Derivative liability, fair value, gross asset	19,650	23,537
Derivative liability	(39)	(595)
Exchange Traded \| J. Aron repurchase obligation derivative \| Fair Value, Measurements, Recurring
Liabilities
Fair value of derivative liability	(19,564)	(20,000)
Derivative liability, fair value, gross asset	0	0
Derivative liability	(19,564)	(20,000)
Exchange Traded \| Fair Value, Inputs, Level 1 \| Future \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	557	190
Liabilities
Fair value of derivative liability	(596)	(54)
Exchange Traded \| Fair Value, Inputs, Level 1 \| J. Aron repurchase obligation derivative \| Fair Value, Measurements, Recurring
Liabilities
Fair value of derivative liability	0	0
Exchange Traded \| Fair Value, Inputs, Level 2 \| Future \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	21,907	26,095
Liabilities
Fair value of derivative liability	(19,093)	(24,078)
Exchange Traded \| Fair Value, Inputs, Level 2 \| J. Aron repurchase obligation derivative \| Fair Value, Measurements, Recurring
Liabilities
Fair value of derivative liability	0	0
Exchange Traded \| Fair Value, Inputs, Level 3 \| Future \| Fair Value, Measurements, Recurring
Assets
Fair value of derivative asset	0	0
Liabilities
Fair value of derivative liability	0	0
Exchange Traded \| Fair Value, Inputs, Level 3 \| J. Aron repurchase obligation derivative \| Fair Value, Measurements, Recurring
Liabilities
Fair value of derivative liability	(19,564)	(20,000)
Over the Counter \| Fair Value, Measurements, Recurring
Liabilities
Common stock warrants	(6,808)	(5,134)
Derivative liability, fair value, gross asset	0	0
Over the Counter \| Fair Value, Inputs, Level 1 \| Fair Value, Measurements, Recurring
Liabilities
Common stock warrants	0	0
Over the Counter \| Fair Value, Inputs, Level 2 \| Fair Value, Measurements, Recurring
Liabilities
Common stock warrants	0	0
Over the Counter \| Fair Value, Inputs, Level 3 \| Fair Value, Measurements, Recurring
Liabilities
Common stock warrants	$ (6,808)	$ (5,134)

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.

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Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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Value of outstanding derivative securities that permit the holder the right to purchase securities (usually equity) from the issuer at a specified price.

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