Investments - Summarized Fair Value and Gross Unrealized Losses on Securities Available for Sale (Detail) $ in Thousands	Sep. 30, 2015 USD ($) Security	Dec. 31, 2014 USD ($) Security
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues | Security	185	108
Less than 12 months, Fair value	$ 170,580	$ 183,191
Less than 12 months, Unrealized losses	$ (2,685)	$ (702)
12 months or longer, Number of issues | Security	15	24
12 months or longer, Fair value	$ 30,921	$ 74,973
12 months or longer, Unrealized losses	$ (3,545)	$ (2,799)
Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues | Security	76	2
Less than 12 months, Fair value	$ 52,514	$ 37,490
Less than 12 months, Unrealized losses	$ (2)	$ (10)
U.S. Government Obligations and Agencies [Member] | Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues | Security		3
Less than 12 months, Fair value		$ 27,341
Less than 12 months, Unrealized losses		$ (55)
12 months or longer, Number of issues | Security	2	4
12 months or longer, Fair value	$ 3,470	$ 34,050
12 months or longer, Unrealized losses	$ (201)	$ (572)
Corporate Bonds [Member] | Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues | Security	58	67
Less than 12 months, Fair value	$ 52,340	$ 58,271
Less than 12 months, Unrealized losses	$ (608)	$ (238)
12 months or longer, Number of issues | Security	4	12
12 months or longer, Fair value	$ 3,952	$ 15,105
12 months or longer, Unrealized losses	$ (41)	$ (126)
Mortgage-Backed and Asset-Backed Securities [Member] | Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues | Security	14	20
Less than 12 months, Fair value	$ 30,805	$ 48,335
Less than 12 months, Unrealized losses	$ (117)	$ (273)
12 months or longer, Number of issues | Security	6	5
12 months or longer, Fair value	$ 15,504	$ 16,842
12 months or longer, Unrealized losses	$ (207)	$ (229)
Redeemable Preferred Stock [Member] | Fixed Maturities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues | Security	30	12
Less than 12 months, Fair value	$ 3,789	$ 1,153
Less than 12 months, Unrealized losses	$ (65)	$ (9)
Common Stock [Member] | Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues | Security	3	2
Less than 12 months, Fair value	$ 8,161	$ 87
Less than 12 months, Unrealized losses	$ (1,168)	$ (20)
12 months or longer, Number of issues | Security	2	2
12 months or longer, Fair value	$ 83	$ 117
12 months or longer, Unrealized losses	$ (106)	$ (45)
Mutual Funds [Member] | Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Less than 12 months, Number of issues | Security	4	2
Less than 12 months, Fair value	$ 22,971	$ 10,514
Less than 12 months, Unrealized losses	$ (725)	$ (97)
12 months or longer, Number of issues | Security	1	1
12 months or longer, Fair value	$ 7,912	$ 8,859
12 months or longer, Unrealized losses	$ (2,990)	$ (1,827)