Investments, Securities with Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available-for-sale securities, continuous unrealized loss position, Fair Value [Abstract]
Less than 12 months	$ 49,234	$ 91,645
12 months or longer	44,198	20,587
Total	93,432	112,232
Available-for-sale Securities, Continuous Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	656	2,985
12 months or longer	3,119	2,556
Total	3,775	5,541
U.S. Treasury Securities and Obligations of U.S. Government Agencies and Authorities [Member]
Available-for-sale securities, continuous unrealized loss position, Fair Value [Abstract]
Less than 12 months	15,900	23,494
12 months or longer	9,016	0
Total	24,916	23,494
Available-for-sale Securities, Continuous Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	188	553
12 months or longer	226	0
Total	414	553
Obligations of States and Political Subdivisions [Member]
Available-for-sale securities, continuous unrealized loss position, Fair Value [Abstract]
Less than 12 months	2,994	8,747
12 months or longer	1,978	0
Total	4,972	8,747
Available-for-sale Securities, Continuous Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	17	308
12 months or longer	37	0
Total	54	308
Corporate Securities [Member]
Available-for-sale securities, continuous unrealized loss position, Fair Value [Abstract]
Less than 12 months	30,340	59,404
12 months or longer	33,204	20,587
Total	63,544	79,991
Available-for-sale Securities, Continuous Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	451	2,124
12 months or longer	2,856	2,556
Total	$ 3,307	$ 4,680