Investments (Amortized Cost and Aggregate Fair Value of Debt Securities, by Contractual Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments [Abstract]
Available-for-sale Securities, Due in one year or less, Amortized Cost	$ 1,284
Available-for-sale Securities, Due in one year or less, Fair Value	1,284
Available-for-sale Securities, Due after one year through five years, Amortized Cost	16,803
Available-for-sale Securities, Due after one year through five years, Fair Value	16,854
Available-for-sale Securities, Due after five years through ten years, Amortized Cost	29,218
Available-for-sale Securities, Due after five years through ten years, Fair Value	29,206
Available-for-sale Securities, Due after ten years, Amortized Cost	48,972
Available-for-sale Securities, Due after ten years, Fair Value	48,481
Available-for-sale securities, Amortized Cost	96,277	$ 94,467
Available-for-sale Securities, Fair Value	95,825
Held-to-maturity Securities, Due in one year or less, Amortized Cost	0
Held-to-maturity Securities, Due in one year or less, Fair Value	0
Held-to-maturity Securities, Due after one year through five years, Amortized Cost	0
Held-to-maturity Securities, Due after one year through five years, Fair Value	0
Held-to-maturity Securities, Due after five years through ten years, Amortized Cost	57
Held-to-maturity Securities, Due after five years through ten years, Fair Value	61
Held-to-maturity Securities, Due after ten years, Amortized Cost	1,516
Held-to-maturity Securities, Due after ten years, Fair Value	1,514
Held-to-maturity Securities, Amortized Cost	1,573	1,616
Held-to-maturity Securities, Fair Value	$ 1,575	$ 1,645