Securities, Available-for-sale Securities (Details) $ in Thousands	Jun. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 Months, Fair Value	$ 10,964	$ 10,119
12 Months or More, Fair Value	1,011
Total, Estimated Fair Value	11,975	10,119
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, Unrealized Losses	132	50
12 Months or More, Unrealized Losses	8
Total, Unrealized Losses	$ 140	50
AFS securities, Number of securities in continuous unrealized loss position | security	10
U.S. Treasury Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 Months, Fair Value	$ 1,973
Total, Estimated Fair Value	1,973
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, Unrealized Losses	14
Total, Unrealized Losses	14
U.S. Government Agency Notes [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract]
Less than 12 Months, Fair Value	8,991	10,119
12 Months or More, Fair Value	1,011
Total, Estimated Fair Value	10,002	10,119
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss [Abstract]
Less than 12 Months, Unrealized Losses	118	50
12 Months or More, Unrealized Losses	8
Total, Unrealized Losses	$ 126	$ 50