SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE - Repurchase Agreements Grouped by Counterparty (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Repurchase Agreement Counterparty [Line Items]
Repurchase agreements, interest ranging from 2.45% to 3.39% (December 31, 2011 - 2.50% to 4.40%) (1)	$ 900,000	[1]	$ 900,000	[1]
Citigroup Global Markets [Member]
Repurchase Agreement Counterparty [Line Items]
Repurchase agreements, interest ranging from 2.45% to 3.39% (December 31, 2011 - 2.50% to 4.40%) (1)	300,000
Weighted-Average Maturity	1 year 7 months 0 days
Jp Morgan Chase [Member]
Repurchase Agreement Counterparty [Line Items]
Repurchase agreements, interest ranging from 2.45% to 3.39% (December 31, 2011 - 2.50% to 4.40%) (1)	200,000
Weighted-Average Maturity	6 years 10 months 0 days
Dean Witter Morgan Stanley [Member]
Repurchase Agreement Counterparty [Line Items]
Repurchase agreements, interest ranging from 2.45% to 3.39% (December 31, 2011 - 2.50% to 4.40%) (1)	100,000
Weighted-Average Maturity	2 years 7 months 0 days
Credit Suisse First Boston [Member]
Repurchase Agreement Counterparty [Line Items]
Repurchase agreements, interest ranging from 2.45% to 3.39% (December 31, 2011 - 2.50% to 4.40%) (1)	$ 300,000
Weighted-Average Maturity	5 years 0 months 0 days

[1] As of March 31, 2015, includes $800 million with an average rate of 2.71% that lenders have the right to call before their contractual maturities at various dates beginning on April 9, 2015. Subsequent to April 9, 2015, no lender has exercised its call option on repurchase agreements. In addition, $700 million is tied to variable rates.