Investments (Narrative) (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Gain (Loss) on Investments [Line Items]
Held-to-maturity securities, unrecognized holding loss		$ 0
Other-than-temporary impairments, available-for-sale securities	$ 0	0
Single Largest Loss Position	88,000	75,000
Second Largest Loss Position	87,000	60,000
Third Largest Loss Position	$ 81,000	$ 53,000
Maximum
Gain (Loss) on Investments [Line Items]
Percent of investment portfolio below investment grade	5.94%