SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE - Schedule of Repurchase Agreement Maturity (Parenthetical) (Detail) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Repurchase Agreement [Line Items]
Securities Sold Under Agreements To Repurchase	[1],[2]	$ 300,000	$ 300,000

[1] As of December 31, 2017, includes $200 million with an average rate of 2.11% that lenders have the right to call before their contractual maturities at various dates beginning on February 6, 2018. Subsequent to December 31, 2017, no lender has exercised its call option on repurchase agreements.

[2] Reported net of securities purchased under agreements to repurchase (reverse repurchase agreements) by counterparty, when applicable, pursuant to ASC 210-20-45-11.