Securities - Net Gains and Losses on Trading Account Securities (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Net gain on sales transactions	$ 552	$ 434	$ 1,058	$ 939
Net mark-to-market gains (losses)	27	23	31	(13)
Net gain (loss) on trading account securities	$ 579	$ 457	$ 1,089	$ 926

This item represents the difference between the gross amount of gains (losses) included in earnings for transfers of securities from the available-for-sale category into the trading category. Such net gain (loss) included in earnings represents the net unrealized gain (loss) which had been included in other comprehensive income and is associated with the securities transferred from the available-for-sale category to the trading category.

No definition available.

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