Investment Securities - Number, fair value and gross unrealized holding losses (Details) $ in Thousands	Dec. 31, 2016 USD ($) investment_security	Dec. 31, 2015 USD ($) investment_security
Number
Less than 12 months | investment_security	215	71
12 months or Longer | investment_security	4	9
Total | investment_security	219	80
Fair Value
Less than 12 months	$ 262,191	$ 121,775
12 months or Longer	16,039	16,284
Total	278,230	138,059
Gross Unrealized Holding Losses
Less than 12 months	(4,984)	(923)
12 months or Longer	(519)	(468)
Total	$ (5,503)	$ (1,391)
Number
Less than 12 months | investment_security	1	1
12 months or Longer | investment_security	0	0
Total | investment_security	1	1
Fair Value
Less than 12 months	$ 7,271	$ 8,330
12 months or Longer	0	0
Total	7,271	8,330
Gross Unrealized Holding Losses
Less than 12 months	(104)	(70)
12 months or Longer	0	0
Total	$ (104)	$ (70)
Total securities
Number, Less than 12 months (in investments) | investment_security	216	72
Number, 12 months or Longer (in investments) | investment_security	4	9
Number, Total (in investments) | investment_security	220	81
Fair Value, Less than 12 months	$ 269,462	$ 130,105
Fair Value, 12 months or Longer	16,039	16,284
Fair Value, Total	285,501	146,389
Gross Unrealized Holding Losses, Less than 12 months	(5,088)	(993)
Gross Unrealized Holding Losses, 12 months or longer	(519)	(468)
Gross Unrealized Holding Losses, Total	$ (5,607)	$ (1,461)
Corporate
Number
Less than 12 months | investment_security	3
12 months or Longer | investment_security	0
Total | investment_security	3
Fair Value
Less than 12 months	$ 7,609
12 months or Longer	0
Total	7,609
Gross Unrealized Holding Losses
Less than 12 months	(205)
12 months or Longer	0
Total	$ (205)
Municipal bonds
Number
Less than 12 months | investment_security	152	32
12 months or Longer | investment_security	0	6
Total | investment_security	152	38
Fair Value
Less than 12 months	$ 85,750	$ 15,516
12 months or Longer	0	3,349
Total	85,750	18,865
Gross Unrealized Holding Losses
Less than 12 months	(1,690)	(61)
12 months or Longer	0	(36)
Total	$ (1,690)	$ (97)
Collateralized mortgage obligation: residential
Number
Less than 12 months | investment_security	5	5
12 months or Longer | investment_security	0	0
Total | investment_security	5	5
Fair Value
Less than 12 months	$ 19,092	$ 22,771
12 months or Longer	0	0
Total	19,092	22,771
Gross Unrealized Holding Losses
Less than 12 months	(173)	(183)
12 months or Longer	0	0
Total	$ (173)	$ (183)
Mortgage-backed securities: residential
Number
Less than 12 months | investment_security	55	34
12 months or Longer | investment_security	4	3
Total | investment_security	59	37
Fair Value
Less than 12 months	$ 149,740	$ 83,488
12 months or Longer	16,039	12,935
Total	165,779	96,423
Gross Unrealized Holding Losses
Less than 12 months	(2,916)	(679)
12 months or Longer	(519)	(432)
Total	$ (3,435)	$ (1,111)
Number
Less than 12 months | investment_security	1	1
12 months or Longer | investment_security	0	0
Total | investment_security	1	1
Fair Value
Less than 12 months	$ 7,271	$ 8,330
12 months or Longer	0	0
Total	7,271	8,330
Gross Unrealized Holding Losses
Less than 12 months	(104)	(70)
12 months or Longer	0	0
Total	$ (104)	$ (70)