Securities (Details 2) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Available-for-sale securities
Less Than 12 Months, Fair Value	$ 813,255	$ 829,108
Less Than 12 Months, Unrealized Losses	11,791	13,945
12 Months or Longer, Fair Value	146,210	150,125
12 Months or Longer, Unrealized Losses	5,453	5,474
Total Fair Value	959,465	979,233
Total Unrealized Losses	17,244	19,419
Held-to-maturity debt securities
Less Than 12 Months, Fair Value	32,563	43,369
Less Than 12 Months, Unrealized Losses	209	286
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total Fair Value	32,563	43,369
Total Unrealized Losses	209	286
Obligations of U.S. Government sponsored entities
Available-for-sale securities
Less Than 12 Months, Fair Value	201,138	208,940
Less Than 12 Months, Unrealized Losses	1,971	2,303
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total Fair Value	201,138	208,940
Total Unrealized Losses	1,971	2,303
Held-to-maturity debt securities
Less Than 12 Months, Fair Value	30,118	40,802
Less Than 12 Months, Unrealized Losses	206	283
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total Fair Value	30,118	40,802
Total Unrealized Losses	206	283
Obligations of U.S. states and political subdivisions
Available-for-sale securities
Less Than 12 Months, Fair Value	47,383	58,852
Less Than 12 Months, Unrealized Losses	744	1,139
12 Months or Longer, Fair Value	0	751
12 Months or Longer, Unrealized Losses	0	1
Total Fair Value	47,383	59,603
Total Unrealized Losses	744	1,140
U.S. Government agencies
Available-for-sale securities
Less Than 12 Months, Fair Value	102,556	98,307
Less Than 12 Months, Unrealized Losses	1,485	1,570
12 Months or Longer, Fair Value	21,325	22,376
12 Months or Longer, Unrealized Losses	675	702
Total Fair Value	123,881	120,683
Total Unrealized Losses	2,160	2,272
U.S. Government sponsored entities
Available-for-sale securities
Less Than 12 Months, Fair Value	462,178	463,009
Less Than 12 Months, Unrealized Losses	7,591	8,933
12 Months or Longer, Fair Value	121,805	123,915
12 Months or Longer, Unrealized Losses	4,357	4,354
Total Fair Value	583,983	586,924
Total Unrealized Losses	11,948	13,287
U.S. corporate debt securities
Available-for-sale securities
Less Than 12 Months, Fair Value	0	0
Less Than 12 Months, Unrealized Losses	0	0
12 Months or Longer, Fair Value	2,163	2,162
12 Months or Longer, Unrealized Losses	338	338
Total Fair Value	2,163	2,162
Total Unrealized Losses	338	338
Equity securities
Available-for-sale securities
Less Than 12 Months, Fair Value	0	0
Less Than 12 Months, Unrealized Losses	0	0
12 Months or Longer, Fair Value	917	921
12 Months or Longer, Unrealized Losses	83	79
Total Fair Value	917	921
Total Unrealized Losses	83	79
Obligations of U.S. states and political subdivisions
Held-to-maturity debt securities
Less Than 12 Months, Fair Value	2,445	2,567
Less Than 12 Months, Unrealized Losses	3	3
12 Months or Longer, Fair Value	0	0
12 Months or Longer, Unrealized Losses	0	0
Total Fair Value	2,445	2,567
Total Unrealized Losses	$ 3	$ 3