Service Agreements and Related Party Transactions - Additional Information (Detail) $ in Thousands		12 Months Ended
	Oct. 14, 2014 Directors	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Related Party Transaction [Line Items]
Payment of stock offering fee				$ 19,310
WMMRC [Member]
Related Party Transaction [Line Items]
Administrative services agreement fee		$ 110
Lawsuit against number of former directors | Directors	16
Litigation settlement amount				37,000
Litigation settlement reserve for reimbursement of contingent fees and expenses				3,000
WMMRC [Member] | Investment Management Agreement And Administrative Services Agreement [Member]
Related Party Transaction [Line Items]
Expenses incurred under the agreements		$ 1,400	$ 1,400	1,400
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.
WMI Holdings Corp [Member]
Related Party Transaction [Line Items]
Litigation settlement reserve for reimbursement of contingent fees and expenses		$ 1,500
Other income		$ 123	$ 123	7,800
KKR Capital Markets LLC [Member] | Redeemable Convertible Series B Preferred Stock [Member]
Related Party Transaction [Line Items]
Payment of stock offering fee				8,250
Payment of additional deferred Fee				$ 8,250