Securities, Securities in Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Securities [Abstract]
Percentage of total investment with unrealized losses	76.00%	69.50%
Available-for-sale, amortized cost [Abstract]
Less than 12 months	$ 309,707	$ 241,239
12 months or more	161,558	173,642
Total	471,265	414,881
Available-for-sale, gross unrealized losses [Abstract]
Less than 12 months	(4,386)	(2,004)
12 months or more	(6,523)	(5,054)
Total	(10,909)	(7,058)
Available-for-sale, fair value [Abstract]
Less than 12 months	305,321	239,235
12 months or more	155,035	168,588
Total	460,356	407,823
U.S. Treasury and Government Agencies [Member]
Available-for-sale, amortized cost [Abstract]
Less than 12 months	191,465	136,688
12 months or more	23,751	23,885
Total	215,216	160,573
Available-for-sale, gross unrealized losses [Abstract]
Less than 12 months	(1,834)	(840)
12 months or more	(524)	(332)
Total	(2,358)	(1,172)
Available-for-sale, fair value [Abstract]
Less than 12 months	189,631	135,848
12 months or more	23,227	23,553
Total	212,858	159,401
State and Political Subdivisions [Member]
Available-for-sale, amortized cost [Abstract]
Less than 12 months	49,584	34,283
12 months or more	18,284	16,930
Total	67,868	51,213
Available-for-sale, gross unrealized losses [Abstract]
Less than 12 months	(1,228)	(416)
12 months or more	(1,526)	(745)
Total	(2,754)	(1,161)
Available-for-sale, fair value [Abstract]
Less than 12 months	48,356	33,867
12 months or more	16,758	16,185
Total	65,114	50,052
U.S. Government Sponsored Agency Mortgage-backed Securities [Member]
Available-for-sale, amortized cost [Abstract]
Less than 12 months	68,658	62,768
12 months or more	119,523	117,827
Total	188,181	180,595
Available-for-sale, gross unrealized losses [Abstract]
Less than 12 months	(1,324)	(643)
12 months or more	(4,473)	(3,364)
Total	(5,797)	(4,007)
Available-for-sale, fair value [Abstract]
Less than 12 months	67,334	62,125
12 months or more	115,050	114,463
Total	182,384	176,588
Debt Securities [Member]
Available-for-sale, amortized cost [Abstract]
Less than 12 months	309,707	233,739
12 months or more	161,558	158,642
Total	471,265	392,381
Available-for-sale, gross unrealized losses [Abstract]
Less than 12 months	(4,386)	(1,899)
12 months or more	(6,523)	(4,441)
Total	(10,909)	(6,340)
Available-for-sale, fair value [Abstract]
Less than 12 months	305,321	231,840
12 months or more	155,035	154,201
Total	460,356	386,041
CRA Investments Funds [Member]
Available-for-sale, amortized cost [Abstract]
Less than 12 months	0	7,500
12 months or more	0	15,000
Total	0	22,500
Available-for-sale, gross unrealized losses [Abstract]
Less than 12 months	0	(105)
12 months or more	0	(613)
Total	0	(718)
Available-for-sale, fair value [Abstract]
Less than 12 months	0	7,395
12 months or more	0	14,387
Total	$ 0	$ 21,782