Retirement Plan - Additional Information (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Distributed shares subject to put option, fair value	$ 348,486,000	$ 425,514,000
ESOP, shares cost	2,773,677,000	2,642,583,000
Common stock related to ESOP	3,122,163,000	3,068,097,000
ESOP shares, fair value	$ 7,173,372,000	$ 8,356,659,000

Carrying amount, attributable to parent, of an entity's issued and outstanding stock which is not included within permanent equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer.

No definition available.

Name:	us-gaap_TemporaryEquityCarryingAmountAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant