Derivative Instruments - Swap Agreements by Counterparty (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Chicago Mercantile Exchange
Derivative [Line Items]
Notional Amount	$ 2,956,000	$ 3,306,000
Interest rate swap agreements
Derivative [Line Items]
Notional Amount	$ 2,956,000	$ 3,306,000

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