Investments - Unrealized losses (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	$ 234,330	$ 283,243
Less than 12 Months, Unrealized Losses	(5,954)	(8,501)
12 Months or More, Fair Value	28,613	18,104
12 Months or More, Unrealized Losses	(276)	(261)
Total Fair Value	262,943	301,347
Total Unrealized Losses	(6,230)	(8,762)
U.S. Government agencies
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	16,341	34,586
Less than 12 Months, Unrealized Losses	(61)	(198)
12 Months or More, Fair Value	21,667	10,438
12 Months or More, Unrealized Losses	(131)	(79)
Total Fair Value	38,008	45,024
Total Unrealized Losses	(192)	(277)
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	95,913	122,522
Less than 12 Months, Unrealized Losses	(2,846)	(4,353)
12 Months or More, Fair Value	0	0
12 Months or More, Unrealized Losses	0	0
Total Fair Value	95,913	122,522
Total Unrealized Losses	(2,846)	(4,353)
U.S. Government agencies collateralized by residential mortgage obligations
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	114,660	118,719
Less than 12 Months, Unrealized Losses	(2,963)	(3,866)
12 Months or More, Fair Value	6,946	7,666
12 Months or More, Unrealized Losses	(145)	(182)
Total Fair Value	121,606	126,385
Total Unrealized Losses	(3,108)	(4,048)
Other equity securities
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	7,416	7,416
Less than 12 Months, Unrealized Losses	(84)	(84)
12 Months or More, Fair Value	0	0
12 Months or More, Unrealized Losses	0	0
Total Fair Value	7,416	7,416
Total Unrealized Losses	$ (84)	$ (84)