Summary of Characteristics of Interest Rate Swaptions (Detail) (Interest Rate Swaption, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013
Long
Derivative Instruments:
Current Underlying Notional	$ 5,150,000
Underlying Pay RateXX	3.07
Underlying Receive Rate	3M LIBO R
Years to Maturity	10 years 1 month 6 days
Months to Expiration	4 months 8 days
Short
Derivative Instruments:
Current Underlying Notional	$ 1,000,000
Underlying Pay RateXX	3M LIBO R
Underlying Receive Rate	2.83
Years to Maturity	5 years 11 months 16 days
Months to Expiration	23 months 22 days