Investments - Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total investments at fair value	$ 130,233	$ 122,275
Level 2 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total investments at fair value	122,859	114,901
Level 3 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total investments at fair value	7,374	7,374
Municipal Bonds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total investments at fair value	8,296	8,863
Municipal Bonds [Member] | Level 2 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total investments at fair value	922	1,489
Municipal Bonds [Member] | Level 3 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total investments at fair value	7,374	7,374
Non-governmental Debt Securities [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total investments at fair value	84,906	76,757
Non-governmental Debt Securities [Member] | Level 2 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total investments at fair value	84,906	76,757
Treasury and Federal Agencies [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total investments at fair value	37,031	36,655
Treasury and Federal Agencies [Member] | Level 2 [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Total investments at fair value	$ 37,031	$ 36,655