Investments (Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
U.S. Treasury obligations [Member]
Fixed maturities, available for sale
Amortized Cost	$ 139,654	$ 122,855
Gross Unrealized Gains	2,719	1,696
Gross Unrealized Losses	59	659
Estimated Fair Value	142,314	123,892
U.S. Government-sponsored enterprise obligations [Member]
Fixed maturities, available for sale
Amortized Cost	29,945	25,456
Gross Unrealized Gains	771	927
Gross Unrealized Losses	0	49
Estimated Fair Value	30,716	26,334
State and municipal bonds [Member]
Fixed maturities, available for sale
Amortized Cost	849,487	904,719
Gross Unrealized Gains	35,828	36,739
Gross Unrealized Losses	777	823
Estimated Fair Value	884,538	940,635
Corporate debt [Member]
Fixed maturities, available for sale
Amortized Cost	1,295,190	1,296,128
Gross Unrealized Gains	44,880	24,720
Gross Unrealized Losses	4,311	29,162
Estimated Fair Value	1,335,759	1,291,686
Residential mortgage-backed securities [Member]
Fixed maturities, available for sale
Amortized Cost	209,708	233,659
Gross Unrealized Gains	7,924	6,039
Gross Unrealized Losses	57	1,311
Estimated Fair Value	217,575	238,387
Agency commercial mortgage-backed securities [Member]
Fixed maturities, available for sale
Amortized Cost	12,958	10,851
Gross Unrealized Gains	285	174
Gross Unrealized Losses	16	26
Estimated Fair Value	13,227	10,999
Other commercial mortgage-backed securities [Member]
Fixed maturities, available for sale
Amortized Cost	20,315	29,983
Gross Unrealized Gains	329	354
Gross Unrealized Losses	9	203
Estimated Fair Value	20,635	30,134
Other asset-backed securities [Member]
Fixed maturities, available for sale
Amortized Cost	105,171	98,412
Gross Unrealized Gains	692	54
Gross Unrealized Losses	26	246
Estimated Fair Value	105,837	98,220
Debt Securities [Member]
Fixed maturities, available for sale
Amortized Cost	2,662,428	2,722,063
Gross Unrealized Gains	93,428	70,703
Gross Unrealized Losses	5,255	32,479
Estimated Fair Value	$ 2,750,601	$ 2,760,287