Investments - Schedule of Fair Value of Financial Instruments Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities
Fair value of financial instruments	$ 783,462	$ 528,647
U.S. Government and Agency Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	198,883	149,952
Foreign Government
Schedule of Available-for-sale Securities
Fair value of financial instruments	2,062	2,061
States, Municipalities and Political Subdivisions
Schedule of Available-for-sale Securities
Fair value of financial instruments	199,015	169,112
Public Utilities
Schedule of Available-for-sale Securities
Fair value of financial instruments	19,208	7,730
Corporate Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	275,293	164,536
Asset-backed Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	20,556
Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Fair value of financial instruments	1,166	1,125
Fixed Maturities
Schedule of Available-for-sale Securities
Fair value of financial instruments	716,183	494,516
Public Utilities
Schedule of Available-for-sale Securities
Fair value of financial instruments	2,812	1,507
Common Stock
Schedule of Available-for-sale Securities
Fair value of financial instruments	26,433	24,048
Nonredeemable Preferred Stocks
Schedule of Available-for-sale Securities
Fair value of financial instruments	1,638	2,843
Equity Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	59,431	28,398
Other Long-term Investments
Schedule of Available-for-sale Securities
Fair value of financial instruments	7,848	5,733
Mutual Fund
Schedule of Available-for-sale Securities
Fair value of financial instruments	28,548
Level 1
Schedule of Available-for-sale Securities
Fair value of financial instruments	60,897	29,823
Level 1 | U.S. Government and Agency Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 1 | Foreign Government
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 1 | States, Municipalities and Political Subdivisions
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 1 | Public Utilities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 1 | Corporate Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 1 | Asset-backed Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0
Level 1 | Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Fair value of financial instruments	1,166	1,125
Level 1 | Fixed Maturities
Schedule of Available-for-sale Securities
Fair value of financial instruments	1,166	1,125
Level 1 | Public Utilities
Schedule of Available-for-sale Securities
Fair value of financial instruments	2,812	1,507
Level 1 | Common Stock
Schedule of Available-for-sale Securities
Fair value of financial instruments	26,433	24,048
Level 1 | Nonredeemable Preferred Stocks
Schedule of Available-for-sale Securities
Fair value of financial instruments	1,638	2,843
Level 1 | Equity Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	59,431	28,398
Level 1 | Other Long-term Investments
Schedule of Available-for-sale Securities
Fair value of financial instruments	300	300
Level 1 | Mutual Fund
Schedule of Available-for-sale Securities
Fair value of financial instruments	28,548
Level 2
Schedule of Available-for-sale Securities
Fair value of financial instruments	721,869	497,126
Level 2 | U.S. Government and Agency Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	198,883	149,952
Level 2 | Foreign Government
Schedule of Available-for-sale Securities
Fair value of financial instruments	2,062	2,061
Level 2 | States, Municipalities and Political Subdivisions
Schedule of Available-for-sale Securities
Fair value of financial instruments	199,015	169,112
Level 2 | Public Utilities
Schedule of Available-for-sale Securities
Fair value of financial instruments	19,208	7,730
Level 2 | Corporate Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	275,293	164,536
Level 2 | Asset-backed Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	20,556
Level 2 | Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 2 | Fixed Maturities
Schedule of Available-for-sale Securities
Fair value of financial instruments	715,017	493,391
Level 2 | Public Utilities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 2 | Common Stock
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 2 | Nonredeemable Preferred Stocks
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 2 | Equity Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 2 | Other Long-term Investments
Schedule of Available-for-sale Securities
Fair value of financial instruments	6,852	3,735
Level 2 | Mutual Fund
Schedule of Available-for-sale Securities
Fair value of financial instruments	0
Level 3
Schedule of Available-for-sale Securities
Fair value of financial instruments	696	1,698
Level 3 | U.S. Government and Agency Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | Foreign Government
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | States, Municipalities and Political Subdivisions
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | Public Utilities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | Corporate Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | Asset-backed Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0
Level 3 | Redeemable Preferred Stocks
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | Fixed Maturities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | Public Utilities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | Common Stock
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | Nonredeemable Preferred Stocks
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | Equity Securities
Schedule of Available-for-sale Securities
Fair value of financial instruments	0	0
Level 3 | Other Long-term Investments
Schedule of Available-for-sale Securities
Fair value of financial instruments	696	$ 1,698
Level 3 | Mutual Fund
Schedule of Available-for-sale Securities
Fair value of financial instruments	$ 0