Service Agreements and Related Party Transactions - Additional Information (Detail) $ / shares in Units, $ in Thousands			6 Months Ended
	Feb. 02, 2015 USD ($)	Oct. 14, 2014 Directors	Jun. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2014 USD ($)	Jan. 05, 2015 USD ($)
Related Party Transaction [Line Items]
Payment of stock offering fee			$ 19,310	$ 3,234
WMMRC [Member]
Related Party Transaction [Line Items]
Administrative services agreement fee			$ 110
Lawsuit against number of former directors | Directors		16
Pro Rata Share of the Common Stock Allotment | shares			10,000,000
Percentage of Pro Rata Share of the Common Stock Election			5.00%
Principal amount of Runoff Notes | $ / shares			$ 1.00
Litigation settlement amount			$ 37,000
Proceeds from litigation settlement amount	$ 9,000		8,300
Litigation settlement reserve for reimbursement of contingent fees and expenses					$ 3,000
Net proceeds from litigation settlement			34,000
WMMRC [Member] | Investment Management Agreement And Administrative Services Agreement [Member]
Related Party Transaction [Line Items]
Expenses incurred under the agreements			$ 700	$ 800
WMMRC [Member] | Investment Management Agreement [Member]
Related Party Transaction [Line Items]
Description of fee			fee equal to the product of (x) the ending dollar amount of assets under management during the calendar month in question and (y) .002 divided by 12.
KKR Capital Markets LLC [Member] | Series B Preferred Stock [Member]
Related Party Transaction [Line Items]
Payment of stock offering fee			$ 8,250
Payment of additional deferred Fee			$ 8,250