Investments - Unrealized losses (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	$ 111,755	$ 283,243
Less than 12 Months, Unrealized Losses	(657)	(8,501)
12 Months or More, Fair Value	92,356	18,104
12 Months or More, Unrealized Losses	(2,674)	(261)
Total Fair Value	204,111	301,347
Total Unrealized Losses	(3,331)	(8,762)
U.S. Government agencies
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	0	34,586
Less than 12 Months, Unrealized Losses	0	(198)
12 Months or More, Fair Value	7,272	10,438
12 Months or More, Unrealized Losses	(47)	(79)
Total Fair Value	7,272	45,024
Total Unrealized Losses	(47)	(277)
Obligations of states and political subdivisions
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	8,239	122,522
Less than 12 Months, Unrealized Losses	(65)	(4,353)
12 Months or More, Fair Value	18,216	0
12 Months or More, Unrealized Losses	(451)	0
Total Fair Value	26,455	122,522
Total Unrealized Losses	(516)	(4,353)
U.S. Government agencies collateralized by residential mortgage obligations
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	54,089	118,719
Less than 12 Months, Unrealized Losses	(199)	(3,866)
12 Months or More, Fair Value	66,868	7,666
12 Months or More, Unrealized Losses	(2,176)	(182)
Total Fair Value	120,957	126,385
Total Unrealized Losses	(2,375)	(4,048)
Private label mortgage backed securities
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	41,941
Less than 12 Months, Unrealized Losses	(379)
12 Months or More, Fair Value	0
12 Months or More, Unrealized Losses	0
Total Fair Value	41,941
Total Unrealized Losses	(379)
Other equity securities
Schedule of Available-for-sale Securities
Less than 12 Months, Fair Value	7,486	7,416
Less than 12 Months, Unrealized Losses	(14)	(84)
12 Months or More, Fair Value	0	0
12 Months or More, Unrealized Losses	0	0
Total Fair Value	7,486	7,416
Total Unrealized Losses	$ (14)	$ (84)