Securities - Securities in Unrealized Loss Positions (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Estimated Fair Value
Less than 12 months	$ 12,478	$ 7,640
12 months or more	771	812
Total	13,249	8,452
Gross Unrealized Losses
Less than 12 months	(249)	(31)
12 months or more	(30)	(17)
Total	(279)	(48)
Federal agency mortgage-backed securities
Estimated Fair Value
Less than 12 months	7,089	4,130
12 months or more	771	812
Total	7,860	4,942
Gross Unrealized Losses
Less than 12 months	(140)	(20)
12 months or more	(30)	(17)
Total	(170)	(37)
Federal agency debt
Estimated Fair Value
Less than 12 months	5,389	3,510
Total	5,389	3,510
Gross Unrealized Losses
Less than 12 months	(109)	(11)
Total	$ (109)	$ (11)