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Investments - Additional Information (Detail) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 8,534	$ 6,899
Gross unrealized losses for 12 months or greater	[1]	340	$ 1,739
Investments in insurance enhanced asset backed and credit securities		45,500
Investments in insurance enhanced municipal bonds		19,005
Ratings without insurance		511
Investments in asset backed and taxable municipal bonds		$ 26,500
Asset backed and taxable municipal bonds as a percentage of total cash and invested assets		1.40%
Municipal Bond Insurance Association
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		$ 8,400
Ambac Financial Group
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		1,400
Assured Guaranty Corporation
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		14,500
Financial Guaranty Insurance Group
Schedule of Available-for-sale Securities [Line Items]
Investments in asset backed and taxable municipal bonds		200
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		$ 10,820
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		$ 8,321
Pre-Refunded Securities | Financial Guarantors
Schedule of Available-for-sale Securities [Line Items]
Investments in insurance enhanced municipal bonds		136
A+ Rating
Schedule of Available-for-sale Securities [Line Items]
Investments in insurance enhanced municipal bonds		$ 19,000
Insurance enhanced municipal bonds as a percentage of total cash and invested assets		0.01%
Insurance enhanced municipal bonds		$ 10,700
Obligations of States and Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		670
Obligations of States and Political Subdivisions | A Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		97
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		1,072
Corporate bonds | BBB Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		21
Common Shares
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		4,950	$ 2,938
Gross unrealized losses for 12 months or greater	[1]		$ 130
U.S. Treasury and Agency Obligations | AA+ Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		9
Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		159
Mortgage Backed Securities | Standard & Poor's, CC Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		45
Asset-backed Securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		616
Gross unrealized losses for 12 months or greater		$ 28
Weighted average credit enhancement		21.90%
Commercial Mortgage-Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 827
Weighted average credit enhancement		35.70%
Percentage of securities in unrealized loss for months position rated		81.00%
Commercial Mortgage-Backed Securities | AA- Rating
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses for 12 months or greater		$ 140
Foreign Corporate Bonds
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized losses		$ 231
[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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