Schedule of Investment Income (Parenthetical) (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Investment expense	[1]	$ 2,472	$ 903	$ 3,203	$ 1,739
Commitment to purchase alternative investment		40,000		40,000		$ 50,000
Upfront Fees
Schedule of Available-for-sale Securities [Line Items]
Investment expense		$ 1,500		$ 1,500

[1] Investment expense for both the quarter and six months ended June 30, 2016 include $1.5 million in upfront fees necessary to enter into a new investment. See Note 9 for additional information on the Company's $40 million commitment related to this new investment.