Fair Value Measurements - Available-for-Sale Securities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Financial Assets:
Total fixed-maturity securities	$ 165,435	$ 97,084
Equity securities	60,331	45,550
Total available-for-sale securities	225,766	142,634
Fair Value, Measurements, Recurring [Member]
Financial Assets:
Cash and cash equivalents	274,729	314,416
Total fixed-maturity securities	165,435	97,084
Equity securities	60,331	45,550
Total available-for-sale securities	225,766	142,634
Total financial assets	500,495	457,050
Fair Value, Measurements, Recurring [Member] | (Level 1) [Member]
Financial Assets:
Cash and cash equivalents	274,729	314,416
Total fixed-maturity securities	55,946	32,900
Equity securities	60,331	45,550
Total available-for-sale securities	116,277	78,450
Total financial assets	391,006	392,866
Fair Value, Measurements, Recurring [Member] | (Level 2) [Member]
Financial Assets:
Total fixed-maturity securities	109,489	64,184
Total available-for-sale securities	109,489	64,184
Total financial assets	109,489	64,184
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | U.S. Treasury and U.S. Government Agencies [Member]
Financial Assets:
Total fixed-maturity securities	10,927	2,878
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | Corporate Bonds [Member]
Financial Assets:
Total fixed-maturity securities	42,405	23,272
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | Asset-backed Securities [Member]
Financial Assets:
Total fixed-maturity securities	4,163	697
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | Mortgage-Backed Securities [Member]
Financial Assets:
Total fixed-maturity securities	14,438	3,009
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | State, Municipalities, and Political Subdivisions [Member]
Financial Assets:
Total fixed-maturity securities	82,537	57,503
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | Redeemable Preferred Stock [Member]
Financial Assets:
Total fixed-maturity securities	10,467	9,557
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | Other [Member]
Financial Assets:
Total fixed-maturity securities	498	168
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | (Level 1) [Member] | U.S. Treasury and U.S. Government Agencies [Member]
Financial Assets:
Total fixed-maturity securities	4,056	1,069
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | (Level 1) [Member] | Corporate Bonds [Member]
Financial Assets:
Total fixed-maturity securities	41,423	22,274
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | (Level 1) [Member] | Redeemable Preferred Stock [Member]
Financial Assets:
Total fixed-maturity securities	10,467	9,557
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | (Level 2) [Member] | U.S. Treasury and U.S. Government Agencies [Member]
Financial Assets:
Total fixed-maturity securities	6,871	1,809
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | (Level 2) [Member] | Corporate Bonds [Member]
Financial Assets:
Total fixed-maturity securities	982	998
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | (Level 2) [Member] | Asset-backed Securities [Member]
Financial Assets:
Total fixed-maturity securities	4,163	697
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | (Level 2) [Member] | Mortgage-Backed Securities [Member]
Financial Assets:
Total fixed-maturity securities	14,438	3,009
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | (Level 2) [Member] | State, Municipalities, and Political Subdivisions [Member]
Financial Assets:
Total fixed-maturity securities	82,537	57,503
Fair Value, Measurements, Recurring [Member] | Fixed-Maturity Securities [Member] | (Level 2) [Member] | Other [Member]
Financial Assets:
Total fixed-maturity securities	$ 498	$ 168