Subsequent Events - Additional Information (Detail) - USD ($)		3 Months Ended		9 Months Ended
	Oct. 29, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Subsequent Event [Line Items]
Net realized investment gain		$ (10,778,000)	$ 1,158,000	$ (7,216,000)	$ 40,226,000
Fox Paine & Company, LLC | Redemption Agreement | Had the redemption occurred on or prior to September 30, 2015
Subsequent Event [Line Items]
Ordinary shares, shares outstanding		17,472,318		17,472,318
Subsequent Events | Fox Paine & Company, LLC | Redemption Agreement
Subsequent Event [Line Items]
Ordinary shares agreed to redeem, shares	8,260,870
Ordinary shares agreed to redeem	$ 190,000,000
Proceeds from sale of securities	279,900,000
Net realized investment gain	1,600,000
Repayments under margin borrowing facilities	$ 102,000,000
Subsequent Events | Fox Paine & Company, LLC | Additional Redemption Agreement
Subsequent Event [Line Items]
Ordinary shares agreed to redeem, shares	3,376,561
Ordinary shares agreed to redeem	$ 77,660,903
Redemption agreement expiration date	Dec. 31, 2019
Subsequent Events | Fox Paine & Company, LLC | Redemption Agreement in Discussions
Subsequent Event [Line Items]
Ordinary shares agreed to redeem, shares	1,146,716