Investment Securities - Number, fair value and gross unrealized holding losses (Details) $ in Thousands	Dec. 31, 2019 USD ($) investment_security	Dec. 31, 2018 USD ($) investment_security
Number
Less than 12 months | investment_security	45	105
12 months or Longer | investment_security	21	244
Total | investment_security	66	349
Fair Value
Less than 12 months	$ 274,640	$ 190,770
12 months or Longer	41,003	442,464
Total	315,643	633,234
Gross Unrealized Holding Losses
Less than 12 months	(3,258)	(1,609)
12 months or Longer	(834)	(12,600)
Total	$ (4,092)	$ (14,209)
Number
Less than 12 months | investment_security	0	3
12 months or Longer | investment_security	0	3
Total | investment_security	0	6
Fair Value
Less than 12 months	$ 0	$ 11,256
12 months or Longer	0	15,741
Total	0	26,997
Gross Unrealized Holding Losses
Less than 12 months	0	(81)
12 months or Longer	0	(605)
Total	$ 0	$ (686)
Total investment securities
Number, Less than 12 months (in investments) | investment_security	45	108
Number, 12 months or Longer (in investments) | investment_security	21	247
Number, Total (in investments) | investment_security	66	355
Fair Value, Less than 12 months	$ 274,640	$ 202,026
Fair Value, 12 months or Longer	41,003	458,205
Fair Value, Total	315,643	660,231
Gross Unrealized Holding Losses, Less than 12 months	(3,258)	(1,690)
Gross Unrealized Holding Losses, 12 months or longer	(834)	(13,205)
Gross Unrealized Holding Losses, Total	$ (4,092)	$ (14,895)
U.S. Treasury
Number
Less than 12 months | investment_security	1	0
12 months or Longer | investment_security	0	0
Total | investment_security	1	0
Fair Value
Less than 12 months	$ 10,194	$ 0
12 months or Longer	0	0
Total	10,194	0
Gross Unrealized Holding Losses
Less than 12 months	(39)	0
12 months or Longer	0	0
Total	$ (39)	$ 0
Agency
Number
Less than 12 months | investment_security	13	15
12 months or Longer | investment_security	9	6
Total | investment_security	22	21
Fair Value
Less than 12 months	$ 102,874	$ 26,229
12 months or Longer	13,514	10,434
Total	116,388	36,663
Gross Unrealized Holding Losses
Less than 12 months	(1,340)	(333)
12 months or Longer	(336)	(186)
Total	$ (1,676)	$ (519)
Corporate debt
Number
Less than 12 months | investment_security	1	9
12 months or Longer | investment_security	0	8
Total | investment_security	1	17
Fair Value
Less than 12 months	$ 1,017	$ 47,805
12 months or Longer	0	19,369
Total	1,017	67,174
Gross Unrealized Holding Losses
Less than 12 months	(14)	(471)
12 months or Longer	0	(435)
Total	$ (14)	$ (906)
Municipal bonds
Number
Less than 12 months | investment_security	12	60
12 months or Longer | investment_security	0	102
Total | investment_security	12	162
Fair Value
Less than 12 months	$ 30,541	$ 45,083
12 months or Longer	0	69,693
Total	30,541	114,776
Gross Unrealized Holding Losses
Less than 12 months	(184)	(369)
12 months or Longer	0	(1,856)
Total	$ (184)	$ (2,225)
Collateralized mortgage obligation: residential
Number
Less than 12 months | investment_security	0	1
12 months or Longer | investment_security	1	8
Total | investment_security	1	9
Fair Value
Less than 12 months	$ 0	$ 814
12 months or Longer	603	18,104
Total	603	18,918
Gross Unrealized Holding Losses
Less than 12 months	0	(1)
12 months or Longer	(8)	(424)
Total	$ (8)	$ (425)
Mortgage-backed securities: residential
Number
Less than 12 months | investment_security	18	20
12 months or Longer | investment_security	11	120
Total | investment_security	29	140
Fair Value
Less than 12 months	$ 130,014	$ 70,839
12 months or Longer	26,886	324,864
Total	156,900	395,703
Gross Unrealized Holding Losses
Less than 12 months	(1,681)	(435)
12 months or Longer	(490)	(9,699)
Total	$ (2,171)	$ (10,134)
Number
Less than 12 months | investment_security	0	3
12 months or Longer | investment_security	0	3
Total | investment_security	0	6
Fair Value
Less than 12 months	$ 0	$ 11,256
12 months or Longer	0	15,741
Total	0	26,997
Gross Unrealized Holding Losses
Less than 12 months	0	(81)
12 months or Longer	0	(605)
Total	$ 0	$ (686)
Other
Number
Less than 12 months | investment_security	0	0
12 months or Longer | investment_security	0	0
Total | investment_security	0	0
Fair Value
Less than 12 months	$ 0	$ 0
12 months or Longer	0	0
Total	0	0
Gross Unrealized Holding Losses
Less than 12 months	0	0
12 months or Longer	0	0
Total	$ 0	$ 0