Secured Financings - Revolving Repurchase Facilities Outstanding (Parenthetical) (Detail) (Revolving Repurchase Facilities [Member]) In Millions, unless otherwise specified	Sep. 30, 2014 JP Morgan [Member] USD ($)	Sep. 30, 2014 JP Morgan [Member] GBP (£)	Sep. 30, 2014 Maximum [Member] JP Morgan [Member] USD ($)	Sep. 30, 2014 Maximum [Member] Morgan Stanley [Member] USD ($)	Sep. 30, 2014 Maximum [Member] Morgan Stanley [Member] GBP (£)
Line of Credit Facility [Line Items]
Facility size	$ 248.5	£ 153.0	$ 250.0	$ 406.0	£ 250.0