Contingencies - Additional Information (Detail) $ in Millions	1 Months Ended	12 Months Ended	24 Months Ended
Jan. 31, 2009 interest_plan	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2008 interest_plan	Dec. 31, 2009 interest_plan
Commitments and Contingencies Disclosure [Abstract]
Rent expense \| $		$ 0.3	$ 0.3	$ 0.3
Number of carried interest plans \| interest_plan	1				1	2
Carried interest rate (as a percent)						15.00%

Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line.

No definition available.

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration