Securities - AFS in an Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($) item
Number of Securities
Unrealized loss for less than twelve months | item	77	68
Unrealized loss for twelve months or longer | item	11	11
Total | item	88	79
Fair Value
Unrealized loss for less than twelve months	$ 400,403	$ 267,719
Unrealized loss for twelve months or longer	25,361	30,877
Estimated Fair Value, Total	425,764	298,596
Unrealized Loss
Unrealized loss for less than twelve months	5,861	5,863
Unrealized loss for twelve months or longer	995	1,223
Total	$ 6,856	$ 7,086
US Treasury Securities
Number of Securities
Unrealized loss for less than twelve months | item	7	7
Total | item	7	7
Fair Value
Unrealized loss for less than twelve months	$ 21,713	$ 21,694
Estimated Fair Value, Total	21,713	21,694
Unrealized Loss
Unrealized loss for less than twelve months	44	44
Total	$ 44	$ 44
Bonds
Number of Securities
Unrealized loss for less than twelve months | item	7	1
Total | item	7	1
Fair Value
Unrealized loss for less than twelve months	$ 74,923	$ 14,908
Estimated Fair Value, Total	74,923	14,908
Unrealized Loss
Unrealized loss for less than twelve months	167	67
Total	$ 167	$ 67
Residential mortgage-backed Securities
Number of Securities
Unrealized loss for less than twelve months | item	16	12
Total | item	16	12
Fair Value
Unrealized loss for less than twelve months	$ 155,596	$ 109,398
Estimated Fair Value, Total	155,596	109,398
Unrealized Loss
Unrealized loss for less than twelve months	3,018	2,941
Total	$ 3,018	$ 2,941
Commercial mortgage-backed securities
Number of Securities
Unrealized loss for less than twelve months | item	2	2
Total | item	2	2
Fair Value
Unrealized loss for less than twelve months	$ 7,100	$ 7,127
Estimated Fair Value, Total	7,100	7,127
Unrealized Loss
Unrealized loss for less than twelve months	40	58
Total	$ 40	$ 58
Collateralized mortgage obligations
Number of Securities
Unrealized loss for less than twelve months | item	17	11
Unrealized loss for twelve months or longer | item	8	8
Total | item	25	19
Fair Value
Unrealized loss for less than twelve months	$ 124,634	$ 91,144
Unrealized loss for twelve months or longer	17,895	19,320
Estimated Fair Value, Total	142,529	110,464
Unrealized Loss
Unrealized loss for less than twelve months	2,332	2,340
Unrealized loss for twelve months or longer	911	866
Total	$ 3,243	$ 3,206
Corporate securities
Number of Securities
Unrealized loss for less than twelve months | item	2	3
Total | item	2	3
Fair Value
Unrealized loss for less than twelve months	$ 3,977	$ 5,899
Estimated Fair Value, Total	3,977	5,899
Unrealized Loss
Unrealized loss for less than twelve months	40	91
Total	$ 40	$ 91
States and political subdivisions
Number of Securities
Unrealized loss for less than twelve months | item	25	32
Unrealized loss for twelve months or longer | item	1	1
Total | item	26	33
Fair Value
Unrealized loss for less than twelve months	$ 12,406	$ 17,549
Unrealized loss for twelve months or longer	457	450
Estimated Fair Value, Total	12,863	17,999
Unrealized Loss
Unrealized loss for less than twelve months	220	322
Unrealized loss for twelve months or longer	9	14
Total	$ 229	$ 336
Equity securities
Number of Securities
Unrealized loss for less than twelve months | item	1
Unrealized loss for twelve months or longer | item	2	2
Total | item	3	2
Fair Value
Unrealized loss for less than twelve months	$ 54
Unrealized loss for twelve months or longer	7,009	$ 11,107
Estimated Fair Value, Total	7,063	11,107
Unrealized Loss
Unrealized loss for twelve months or longer	75	343
Total	$ 75	$ 343