Derivative Financial Instruments - Additional Information (Detail)	Sep. 30, 2017 USD ($)
Nondesignated
Derivative Instruments, Gain (Loss) [Line Items]
Derivative financial instruments held, notional amount	$ 765,886,000

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

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

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant