Senior Debt - Summary of Debt (Parenthetical) (Detail) - Term Loan [Member] $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Debt Instrument, Redemption, through September 2017 [Member]
Debt Instrument [Line Items]
Outstanding borrowings, quarterly principal installments payable amount	$ 1.5
Term loans, year of maturity	2017-09
Debt Instrument, Redemption, through September 2018 [Member]
Debt Instrument [Line Items]
Outstanding borrowings, quarterly principal installments payable amount	$ 2.0
Term loans, year of maturity	2018-09
Debt Instrument, Redemption, through September 2020 [Member]
Debt Instrument [Line Items]
Outstanding borrowings, quarterly principal installments payable amount	$ 2.5
Term loans, year of maturity	2020-09