Borrowings Under Repurchase Agreements - Weighted Average Maturities and Interest Rates of Borrowings (Detail) (USD $) In Thousands, unless otherwise specified		9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended
Sep. 30, 2014	Sep. 30, 2014 Line of Credit [Member]	Dec. 31, 2013 Line of Credit [Member]	Sep. 30, 2014 Line of Credit [Member] DB Facility [Member]	Dec. 31, 2013 Line of Credit [Member] DB Facility [Member]	Sep. 30, 2014 Line of Credit [Member] Wells Fargo [Member]	Dec. 31, 2013 Line of Credit [Member] Wells Fargo [Member]	Feb. 28, 2014 Line of Credit [Member] Wells Fargo [Member] One Month LIBOR [Member]	Dec. 31, 2013 Line of Credit [Member] Wells Fargo [Member] One Month LIBOR [Member]	Sep. 30, 2014 Line of Credit [Member] UBS [Member]	Dec. 31, 2013 Line of Credit [Member] UBS [Member]	Sep. 30, 2014 Line of Credit [Member] JP Morgan Chase [Member]	Dec. 31, 2013 Line of Credit [Member] JP Morgan Chase [Member]	Sep. 30, 2014 Line of Credit [Member] JP Morgan Chase [Member] One Month LIBOR [Member]	Sep. 30, 2014 Minimum [Member] Line of Credit [Member] DB Facility [Member] Three Month LIBOR [Member]	Sep. 30, 2014 Maximum [Member] Line of Credit [Member] DB Facility [Member] Three Month LIBOR [Member]
Debt Instrument [Line Items]
Debt Balance	$ 537,766	$ 537,766	$ 202,033	$ 260,155	$ 0	$ 20,990	$ 47,751			$ 133,899	$ 133,899	$ 122,722	$ 20,383
Weighted Average Remaining Maturity		2 years 9 months 18 days	3 years 3 months 12 days	3 years 6 months	0 years	4 months 24 days	2 months 12 days			4 years	4 years 8 months 12 days	3 months 18 days	1 year 1 month 6 days
Weighted Average Rate		3.20%	2.40%	3.80%	0.00%	1.00%	1.20%			2.80%	2.80%	2.70%	2.70%
Basis point								0.80%	1.05%					2.50%	1.80%	2.32%

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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