Debt Obligations - Repurchase Obligations Outstanding (Parenthetical) (Detail) (Repurchase Agreements [Member], USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Revolving Repurchase Facilities [Member]
Credit Facilities [Line Items]
Potential borrowings	$ 683,858
Revolving Repurchase Facilities [Member] | JP Morgan [Member]
Credit Facilities [Line Items]
Facility Size	250,000
Potential borrowings	296,760
Asset-Specific Repurchase Agreements [Member]
Credit Facilities [Line Items]
Potential borrowings	1,018,579
Asset-Specific Repurchase Agreements [Member] | JP Morgan [Member]
Credit Facilities [Line Items]
Facility Size	112,000
Repurchase Date	Jun. 27, 2014
Asset-Specific Repurchase Agreements [Member] | Wells Fargo [Member]
Credit Facilities [Line Items]
Potential borrowings	334,721
Number of asset-specific repurchase agreements	3
Collateral Assets [Member] | Asset-Specific Repurchase Agreements [Member] | Wells Fargo [Member]
Credit Facilities [Line Items]
Potential borrowings	$ 31,000