Investments - Additional Information (Detail) - USD ($)		Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses less than 12 months		$ 8,533,000	$ 14,772,000
Gross unrealized losses		9,424,000	15,287,000
Gross unrealized losses for 12 months or greater	[1]	891,000	$ 515,000
Investments in insurance enhanced asset backed and credit securities		27,100,000
Investments in insurance enhanced municipal bonds		9,810,000
Ratings without insurance		0
Investments in asset backed and taxable municipal bonds		$ 17,300,000
Asset backed and taxable municipal bonds as a percentage of total cash and invested assets		1.20%
Municipal Bond Insurance Association
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		$ 3,000,000
Assured Guaranty Corporation
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		$ 14,300,000
Maximum
Schedule of Available-for-sale Securities [Line Items]
Investments in a single issuer as a percentage of shareholders' equity		5.00%	5.00%
Financial Guarantors
Schedule of Available-for-sale Securities [Line Items]
Investments in insurance enhanced municipal bonds		$ 4,646,000
Taxable Municipal Bonds
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		17,200,000
Pre-Refunded Securities
Schedule of Available-for-sale Securities [Line Items]
Investments in insurance enhanced municipal bonds		5,614,000
Pre-Refunded Securities | Financial Guarantors
Schedule of Available-for-sale Securities [Line Items]
Investments in insurance enhanced municipal bonds		450,000
A+ Rating
Schedule of Available-for-sale Securities [Line Items]
Investments in insurance enhanced municipal bonds		$ 9,800,000
Insurance enhanced municipal bonds as a percentage of total cash and invested assets		0.70%
Tax free insurance enhanced municipal bonds		$ 4,200,000
Common Shares
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses less than 12 months		2,403,000	$ 5,960,000
Gross unrealized losses		2,403,000	5,960,000
Asset-backed Securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 583,000
Weighted average credit enhancement		21.80%
Investments in asset backed and taxable municipal bonds		$ 100,000
Asset-backed Securities | AA Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		90,000
Obligations of States and Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		379,000
Obligations of States and Political Subdivisions | A Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		10,000
U.S. Treasury and Agency Obligations | AA+ Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses less than 12 months		233,000
Mortgage Backed Securities | Investment Grade Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		558,000
Gross unrealized losses for 12 months or greater		17,000
Commercial Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 1,747,000
Weighted average credit enhancement		30.20%
Commercial Mortgage-Backed Securities | A+ Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		$ 657,000
Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		2,848,000
Corporate Bonds | Investment Grade Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		117,000
Foreign Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		673,000
One of the Company's variable interest VIE's, invests in distressed securities and assets
Schedule of Available-for-sale Securities [Line Items]
Significant variable interest in fair value of the non-consolidated VIE		32,900,000	32,600,000
Variable interest entities, maximum exposure to loss		48,600,000	$ 52,600,000
New variable interest VIE
Schedule of Available-for-sale Securities [Line Items]
Significant variable interest in fair value of the non-consolidated VIE		33,200,000
Variable interest entities, maximum exposure to loss		$ 42,300,000

[1] Fixed maturities in a gross unrealized loss position for twelve months or longer are primarily comprised of non-credit losses on investment grade securities where management does not intend to sell, and it is more likely than not that the Company will not be forced to sell the security before recovery. The Company has analyzed these securities and has determined that they are not other than temporarily impaired.