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Investments - Additional Information (Detail) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 5,546	$ 6,899
Gross unrealized losses less than 12 months		5,062	5,160	[1]
Gross unrealized losses for 12 months or greater	[1]	484	$ 1,739
Investments in insurance enhanced asset backed and credit securities		41,100
Investments in insurance enhanced municipal bonds		17,454
Ratings without insurance		515
Investments in asset backed and taxable municipal bonds		$ 23,600
Asset backed and taxable municipal bonds as a percentage of total cash and invested assets		1.30%
Municipal Bond Insurance Association
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		$ 8,800
Ambac Financial Group
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		1,500
Assured Guaranty Corporation
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		11,000
Financial Guaranty Insurance Group
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		300
Build America Mutual
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		2,000
Financial Guarantors
Schedule of Available-for-sale Securities [Line Items]
Investments in insurance enhanced municipal bonds		$ 11,091
Maximum
Schedule of Available-for-sale Securities [Line Items]
Investments in a single issuer as a percentage of shareholders' equity		4.00%	4.00%
Pre-Refunded Securities
Schedule of Available-for-sale Securities [Line Items]
Investments in insurance enhanced municipal bonds		$ 6,501
Pre-Refunded Securities | Financial Guarantors
Schedule of Available-for-sale Securities [Line Items]
Investments in insurance enhanced municipal bonds		138
A+ Rating
Schedule of Available-for-sale Securities [Line Items]
Investments in insurance enhanced municipal bonds		$ 17,500
Insurance enhanced municipal bonds as a percentage of total cash and invested assets		1.00%
Insurance enhanced municipal bonds		$ 11,000
U.S. Treasury and Agency Obligations
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses less than 12 months		1
U.S. Treasury and Agency Obligations | AA+ Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		44
Obligations of States and Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		850
Obligations of States and Political Subdivisions | A Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		134
Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		480
Mortgage Backed Securities | AA+ Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		$ 123
Percentage of securities in unrealized loss position for twelve months or longer and rated investment grade		97.60%
Asset-backed Securities | A Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 193
Weighted average credit enhancement		22.60%
Commercial Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 614
Weighted average credit enhancement		38.20%
Commercial Mortgage-Backed Securities | AA- Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		$ 166
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		463
Corporate bonds | BBB Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		17
Foreign Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 625
Percentage of securities in unrealized loss position less than twelve months and rated investment grade		96.20%
Common Shares
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 2,277	$ 2,938
Gross unrealized losses less than 12 months		$ 2,277	2,808	[1]
Gross unrealized losses for 12 months or greater	[1]		$ 130
[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.

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