Bank Borrowings - Additional Information (Detail) - USD ($)		1 Months Ended	6 Months Ended
	Jul. 27, 2015	Jul. 31, 2015	Jun. 30, 2015	Jul. 30, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Line of credit facility, amount outstanding			$ 95,000,000		$ 25,000,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit amendment date			Jul. 27, 2015
Line of credit, maximum borrowing capacity			$ 100,000,000
Line of credit facility, amount outstanding			$ 95,000,000
Line of credit, weighted average interest rate			2.75%
Revolving Credit Facility | Subsequent Event
Line of Credit Facility [Line Items]
Line of credit facility, amount outstanding				$ 88,000,000
Repayment of unsecured revolving credit facility		$ 7,000,000
Fourth Amendment | Revolving Credit Facility | Subsequent Event
Line of Credit Facility [Line Items]
Line of credit, maximum borrowing capacity	$ 90,000,000
Revolving credit facility, maturity date	Dec. 31, 2018
Asset coverage ratio	125.00%
Capital expenditures	$ 65,000,000
Proforma liquidity	$ 15,000,000
Fourth Amendment | Revolving Credit Facility | Subsequent Event | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Revolving Credit Facility, percentage points added to the reference rate	4.00%