Investments (Details 3) $ in Thousands	Dec. 31, 2017 USD ($) Holdings	Dec. 31, 2016 USD ($) Holdings
Fair value
Less than 12 months	$ 282,770	$ 269,475
12 months or longer	66,019	22,193
Total	348,789	291,668
Unrealized losses
Less than 12 months	2,238	4,116
12 months or longer	1,407	1,047
Total	$ 3,645	$ 5,163
No. of holdings | Holdings	417	253
Investment grade
Fair value
Less than 12 months	$ 214,586	$ 239,041
12 months or longer	62,193	16,061
Total	276,779	255,102
Unrealized losses
Less than 12 months	1,064	3,605
12 months or longer	985	399
Total	$ 2,049	$ 4,004
No. of holdings | Holdings	158	136
Non-investment grade
Fair value
Less than 12 months	$ 57,447	$ 24,484
12 months or longer	3,826	6,132
Total	61,273	30,616
Unrealized losses
Less than 12 months	1,074	309
12 months or longer	422	648
Total	$ 1,496	$ 957
No. of holdings | Holdings	253	116
Fixed maturities
Fair value
Less than 12 months	$ 272,033	$ 263,525
12 months or longer	66,019	22,193
Total	338,052	285,718
Unrealized losses
Less than 12 months	2,138	3,914
12 months or longer	1,407	1,047
Total	$ 3,545	$ 4,961
No. of holdings | Holdings	411	252
U.S. treasury
Fair value
Less than 12 months	$ 10,237	$ 5,031
12 months or longer	1,497	0
Total	11,734	5,031
Unrealized losses
Less than 12 months	110	62
12 months or longer	29	0
Total	$ 139	$ 62
No. of holdings | Holdings	4	1
States & political subdivisions
Fair value
Less than 12 months	$ 52,553	$ 84,611
12 months or longer	14,361	0
Total	66,914	84,611
Unrealized losses
Less than 12 months	288	2,293
12 months or longer	332	0
Total	$ 620	$ 2,293
No. of holdings | Holdings	33	40
Corporate debt securities
Fair value
Less than 12 months	$ 171,154	$ 112,453
12 months or longer	31,113	8,692
Total	202,267	121,145
Unrealized losses
Less than 12 months	1,585	987
12 months or longer	339	399
Total	$ 1,924	$ 1,386
No. of holdings | Holdings	331	155
Residential mortgage-backed securities
Fair value
Less than 12 months	$ 4,156	$ 7,451
12 months or longer	7,064	4,974
Total	11,220	12,425
Unrealized losses
Less than 12 months	29	60
12 months or longer	95	131
Total	$ 124	$ 191
No. of holdings | Holdings	11	13
Commercial mortgage-backed securities
Fair value
Less than 12 months	$ 10,836	$ 26,509
12 months or longer	11,984	4,319
Total	22,820	30,828
Unrealized losses
Less than 12 months	85	437
12 months or longer	612	496
Total	$ 697	$ 933
No. of holdings | Holdings	19	28
Collateralized debt obligations
Fair value
Less than 12 months	$ 21,598	$ 27,470
12 months or longer	0	4,208
Total	21,598	31,678
Unrealized losses
Less than 12 months	41	75
12 months or longer	0	21
Total	$ 41	$ 96
No. of holdings | Holdings	12	15
Other debt securities
Fair value
Less than 12 months	$ 1,499
12 months or longer	0
Total	1,499
Unrealized losses
Less than 12 months	0
12 months or longer	0
Total	$ 0
No. of holdings | Holdings	1
Nonredeemable preferred stock
Fair value
Less than 12 months	$ 10,737
12 months or longer	0
Total	10,737
Unrealized losses
Less than 12 months	100
12 months or longer	0
Total	$ 100
No. of holdings | Holdings	6
Common stock
Fair value
Less than 12 months		$ 5,950
12 months or longer		0
Total		5,950
Unrealized losses
Less than 12 months		202
12 months or longer		0
Total		$ 202
No. of holdings | Holdings		1