Securities - Additional Information (Detail) $ in Thousands	3 Months Ended
Jun. 30, 2018 USD ($)
Mortgage-Backed Securities [Member]
Investment [Line Items]
Reclassification adjustment securities	$ 76,518,180

The amount of a reclassification adjustment made to prior period financial statement amounts.

No definition available.

Name:	us-gaap_PriorPeriodReclassificationAdjustment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration