SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE - Repurchase Agreements Grouped by Counterparty (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Repurchase Agreement Counterparty [Line Items]
Maximum aggregate balance outstanding	$ 900,000	[1]	$ 900,000	[1]
Citigroup Global Markets [Member]
Repurchase Agreement Counterparty [Line Items]
Maximum aggregate balance outstanding	300,000
Weighted-Average Maturity	1 year 9 months 29 days
Jp Morgan Chase [Member]
Repurchase Agreement Counterparty [Line Items]
Maximum aggregate balance outstanding	200,000
Weighted-Average Maturity	2 years 2 months 1 day
Dean Witter Morgan Stanley [Member]
Repurchase Agreement Counterparty [Line Items]
Maximum aggregate balance outstanding	100,000
Weighted-Average Maturity	2 years 9 months 29 days
Credit Suisse First Boston [Member]
Repurchase Agreement Counterparty [Line Items]
Maximum aggregate balance outstanding	$ 300,000
Weighted-Average Maturity	3 years 0 months 0 days

[1] As of December 31, 2014, includes $800 million with an average rate of 3.30%, and that lenders have the right to call before their contractual maturitiesat various dates beginning on January 9, 2015. Subsequent to December 31, 2014, no lender has exercised its call option on repurchase agreements.In addition, $500 million of the $900 million is tied to variable rates.