Securities, Amortized Cost and Fair Value of Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available-for-sale debt securities [Abstract]
Amortized cost	$ 579,413	$ 583,939
Gross unrealized gains	3,500	3,158
Gross unrealized losses	(4,400)	(6,061)
Fair value	578,513	581,036
Available-for-sale [Abstract]
Amortized cost	604,413	608,939
Gross unrealized gains	3,593	3,234
Gross unrealized losses	(4,973)	(6,779)
Fair value	603,033	605,394
Held-to-maturity [Abstract]
Amortized cost	858	866
Gross unrealized gains	0	1
Gross unrealized losses	0	0
Fair value	858	867
U.S. Treasury and Government Agencies [Member]
Available-for-sale debt securities [Abstract]
Amortized cost	218,107	223,014
Gross unrealized gains	239	193
Gross unrealized losses	(488)	(743)
Fair value	217,858	222,464
State and Political Subdivisions [Member]
Available-for-sale debt securities [Abstract]
Amortized cost	134,840	133,351
Gross unrealized gains	2,670	1,957
Gross unrealized losses	(853)	(1,792)
Fair value	136,657	133,516
U.S. Government Sponsored Agency Mortgage-backed Securities [Member]
Available-for-sale debt securities [Abstract]
Amortized cost	226,466	227,574
Gross unrealized gains	591	1,008
Gross unrealized losses	(3,059)	(3,526)
Fair value	223,998	225,056
CRA Investments Funds [Member]
Available-for-sale equity securities [Abstract]
Amortized cost	25,000	25,000
Gross unrealized gains	93	76
Gross unrealized losses	(573)	(718)
Fair value	24,520	24,358
State and Political Subdivisions [Member]
Held-to-maturity [Abstract]
Amortized cost	858	866
Gross unrealized gains	0	1
Gross unrealized losses	0	0
Fair value	$ 858	$ 867