Investments - Available-for-sale Securities in Unrealized Loss Positions (Details) $ in Thousands	Jun. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, number of issues | security		110
Greater than 12 months, number of issues | security		59
Total Number of Issues | security		169
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value		$ 53,517
Greater than 12 months, fair value		37,028
Total Fair Value		90,545
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized losses		(301)
Greater than 12 months, unrealized losses		(880)
Total Unrealized losses		$ (1,181)
Asset-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, number of issues | security	32	20
Greater than 12 months, number of issues | security	3	3
Total Number of Issues | security	35	23
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	$ 17,619	$ 13,948
Greater than 12 months, fair value	558	915
Total Fair Value	18,177	14,863
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized losses	(145)	(29)
Greater than 12 months, unrealized losses	(8)	(6)
Total Unrealized losses	$ (153)	$ (35)
Corporate debt
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, number of issues | security	55	38
Greater than 12 months, number of issues | security	8	10
Total Number of Issues | security	63	48
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	$ 17,978	$ 15,236
Greater than 12 months, fair value	5,481	6,555
Total Fair Value	23,459	21,791
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized losses	(327)	(46)
Greater than 12 months, unrealized losses	(412)	(163)
Total Unrealized losses	$ (739)	$ (209)
State and local government
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, number of issues | security	36	10
Greater than 12 months, number of issues | security	7	7
Total Number of Issues | security	43	17
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	$ 9,190	$ 3,511
Greater than 12 months, fair value	1,371	1,424
Total Fair Value	10,561	4,935
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized losses	(163)	(20)
Greater than 12 months, unrealized losses	(58)	(34)
Total Unrealized losses	$ (221)	$ (54)
U.S. Government
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, number of issues | security	13	12
Greater than 12 months, number of issues | security	6	7
Total Number of Issues | security	19	19
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	$ 13,457	$ 11,555
Greater than 12 months, fair value	1,958	2,207
Total Fair Value	15,415	13,762
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized losses	(218)	(64)
Greater than 12 months, unrealized losses	(48)	(35)
Total Unrealized losses	$ (266)	$ (99)
Mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, number of issues | security	19	6
Greater than 12 months, number of issues | security	27	26
Total Number of Issues | security	46	32
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	$ 8,208	$ 4,935
Greater than 12 months, fair value	22,162	24,939
Total Fair Value	30,370	29,874
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized losses	(223)	(19)
Greater than 12 months, unrealized losses	(1,108)	(503)
Total Unrealized losses	$ (1,331)	$ (522)
Commercial mortgage-backed securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, number of issues | security	4	3
Greater than 12 months, number of issues | security	2	2
Total Number of Issues | security	6	5
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	$ 2,718	$ 2,026
Greater than 12 months, fair value	659	722
Total Fair Value	3,377	2,748
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized losses	(37)	(12)
Greater than 12 months, unrealized losses	(59)	(32)
Total Unrealized losses	$ (96)	$ (44)
Collateralized mortgage obligations
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, number of issues | security	10	8
Greater than 12 months, number of issues | security	0	0
Total Number of Issues | security	10	8
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	$ 1,881	$ 1,870
Greater than 12 months, fair value	0	0
Total Fair Value	1,881	1,870
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized losses	(63)	(36)
Greater than 12 months, unrealized losses	0	0
Total Unrealized losses	$ (63)	$ (36)
Equity securities
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, number of issues | security		13
Greater than 12 months, number of issues | security		4
Total Number of Issues | security		17
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value		$ 436
Greater than 12 months, fair value		266
Total Fair Value		702
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized losses		(75)
Greater than 12 months, unrealized losses		(107)
Total Unrealized losses		$ (182)
Total debt securities available for sale
Available-for-sale Securities, Continuous Unrealized Loss Position, Qualitative Disclosure [Abstract]
Less than 12 months, number of issues | security	169	97
Greater than 12 months, number of issues | security	53	55
Total Number of Issues | security	222	152
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months, fair value	$ 71,051	$ 53,081
Greater than 12 months, fair value	32,189	36,762
Total Fair Value	103,240	89,843
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract]
Less than 12 months, unrealized losses	(1,176)	(226)
Greater than 12 months, unrealized losses	(1,693)	(773)
Total Unrealized losses	$ (2,869)	$ (999)