Securities - HTM in an Unrealized Loss Position (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($) item
Number of Securities
Unrealized loss for less than twelve months | item	9	42
Unrealized loss for twelve months or longer | item		1
Total | item	9	43
Fair Value
Unrealized loss for less than twelve months	$ 10,820	$ 223,113
Unrealized loss for twelve months or longer		2,664
Total	10,820	225,777
Unrealized Losses
Unrealized loss for less than twelve months	20	1,499
Unrealized loss for twelve months or longer		8
Total	$ 20	$ 1,507
U.S. Treasury securities
Number of Securities
Unrealized loss for less than twelve months | item		1
Total | item		1
Fair Value
Unrealized loss for less than twelve months		$ 25,115
Total		25,115
Unrealized Losses
Unrealized loss for less than twelve months		30
Total		$ 30
Bonds
Number of Securities
Unrealized loss for less than twelve months | item		6
Total | item		6
Fair Value
Unrealized loss for less than twelve months		$ 46,607
Total		46,607
Unrealized Losses
Unrealized loss for less than twelve months		372
Total		$ 372
Commercial mortgage-backed securities
Number of Securities
Unrealized loss for less than twelve months | item	1	7
Total | item	1	7
Fair Value
Unrealized loss for less than twelve months	$ 1,416	$ 16,098
Total	1,416	16,098
Unrealized Losses
Unrealized loss for less than twelve months	10	92
Total	$ 10	$ 92
Collateralized mortgage obligations
Number of Securities
Unrealized loss for less than twelve months | item	1	10
Total | item	1	10
Fair Value
Unrealized loss for less than twelve months	$ 6,648	$ 127,393
Total	6,648	127,393
Unrealized Losses
Unrealized loss for less than twelve months	2	970
Total	$ 2	$ 970
States and political subdivisions
Number of Securities
Unrealized loss for less than twelve months | item	7	18
Unrealized loss for twelve months or longer | item		1
Total | item	7	19
Fair Value
Unrealized loss for less than twelve months	$ 2,756	$ 7,900
Unrealized loss for twelve months or longer		2,664
Total	2,756	10,564
Unrealized Losses
Unrealized loss for less than twelve months	8	35
Unrealized loss for twelve months or longer		8
Total	$ 8	$ 43