SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE - Securities Sold Under Agreements to Repurchase (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Securities Sold Under Agreements To Repurchase [Line Items]
Weighted-average interest rates on repurchase agreements	2.46%		1.92%
Securities Sold Under Agreements To Repurchase	$ 150,086		$ 300,000
Callable Repurchase Agreements
Securities Sold Under Agreements To Repurchase [Line Items]
Weighted-average interest rates on repurchase agreements		1.96%
Securities Sold Under Agreements To Repurchase		$ 100,000
short term debt [member]
Securities Sold Under Agreements To Repurchase [Line Items]
Weighted-average interest rates on repurchase agreements	2.85%		1.53%
Securities Sold Under Agreements To Repurchase	$ 50,086		$ 100,000
long term debt [member]
Securities Sold Under Agreements To Repurchase [Line Items]
Weighted-average interest rates on repurchase agreements	2.26%
Securities Sold Under Agreements To Repurchase	$ 100,000		200,000
Maximum [Member]
Securities Sold Under Agreements To Repurchase [Line Items]
Securities Sold Under Agreements To Repurchase	$ 200,000		$ 300,000
Maximum [Member] | long term debt [member]
Securities Sold Under Agreements To Repurchase [Line Items]
Weighted-average interest rates on repurchase agreements			2.26%
Minimum [Member] | long term debt [member]
Securities Sold Under Agreements To Repurchase [Line Items]
Weighted-average interest rates on repurchase agreements			1.96%