Securities - Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Securities
Percentage of investment portfolio	33.00%	73.00%
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Less than 12 Months	$ 95,772	$ 47,880
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, 12 Months or Longer		192,275
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	95,772	240,155
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, Less than 12 Months	39	202
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, 12 Months or Longer		880
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, Total	39	1,082
Treasury notes.
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Less than 12 Months		1,990
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, 12 Months or Longer		995
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total		2,985
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, Less than 12 Months		8
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, 12 Months or Longer		5
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, Total		13
Federal agencies
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Less than 12 Months	94,963	28,296
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, 12 Months or Longer		191,280
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	94,963	219,576
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, Less than 12 Months	37	97
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, 12 Months or Longer		875
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, Total	37	972
Municipals
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Less than 12 Months		2,051
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total		2,051
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, Less than 12 Months		18
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, Total		18
Mortgage-backed - Government-sponsored entity (GSE) - residential
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value
Available-for-sale securities, Continuous Unrealized Loss Position, Fair Value, Less than 12 Months	809	15,543
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value, Total	809	15,543
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, Less than 12 Months	2	79
Available-for-sale securities, Continuous Unrealized Loss Position, Gross Unrealized Losses, Total	$ 2	$ 79