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Derivatives - Credit Value Adjustment Recorded Related to Notional Amount of Derivatives Outstanding (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Credit value adjustment	$ (791)	$ (317)
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, notional amount	401,304	345,102
Not Designated as Hedging Instrument [Member] | Interest Rate Cap [Member]
Derivative [Line Items]
Derivative, notional amount	46,444	14,762
Not Designated as Hedging Instrument [Member] | Credit Default Swap, Buying Protection [Member]
Derivative [Line Items]
Derivative, notional amount	197,660	174,213
Not Designated as Hedging Instrument [Member] | Credit Default Swap, Selling Protection [Member]
Derivative [Line Items]
Derivative, Sold Protection Notional Amount	(46,170)	(40,281)
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Fair value adjustment	459	(443)
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, notional amount	150,000	200,000
Designated as Hedging Instrument [Member] | Forward Contracts [Member]
Derivative [Line Items]
Derivative, notional amount	17,000	0
Fair value adjustment	19	0
Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member]
Derivative [Line Items]
Derivative, notional amount	10,077	4,749
Fair value adjustment	$ (70)	$ (8)

X

- Definition

Derivative, Sold Protection Notional Amount

+ References

No definition available.

+ Details

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X

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

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Period Type:	instant

X

- Definition

Amount of credit risk valuation adjustment to derivative liabilities to properly reflect the credit quality of the entity.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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X

- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Details

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- Details

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- Details

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- Details

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- Details

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