Borrowings Under Repurchase Agreements - Summary of Outstanding Balances, Maximum and Average Balances of Borrowings (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2014	Dec. 31, 2013
Line of Credit Facility [Line Items]
Line of credit, amount outstanding	$ 537,766
Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit, amount outstanding	537,766	202,033
Wells Fargo [Member] \| Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit, amount outstanding	20,990	47,751
Maximum Month-End Balance	47,751
Average Month-End Balance	31,436
UBS [Member] \| Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit, amount outstanding	133,899	133,899
Maximum Month-End Balance	133,899
Average Month-End Balance	133,899
DB Facility [Member] \| Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit, amount outstanding	260,155	0
Maximum Month-End Balance	260,155
Average Month-End Balance	99,611
JP Morgan Chase [Member] \| Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of credit, amount outstanding	122,722	20,383
Maximum Month-End Balance	169,066
Average Month-End Balance	$ 92,026

- 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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