Investment Securities - Amortized Cost and Approximate Fair Values of Securities (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Total available for sale
Amortized Cost	$ 696,189,000	$ 640,499,000
Gross Unrealized Gains	10,347,000	18,479,000
Gross Unrealized Losses	9,674,000	578,000
Investment securities available for sale	696,862,000	658,400,000
Total held to maturity
Amortized Cost	607,643,000	618,599,000
Gross Unrealized Gains	8,092,000	14,583,000
Gross Unrealized Losses	3,802,000	802,000
Fair Value	611,933,000	632,380,000
Total Investment Securities
Amortized Cost	1,303,832,000	1,259,098,000
Gross Unrealized Gains	18,439,000	33,062,000
Gross Unrealized Losses	13,476,000	1,380,000
Fair Value	1,308,795,000	1,290,780,000
U.S. Government-sponsored agency securities
Total available for sale
Amortized Cost	100,000	100,000
Gross Unrealized Gains		4,000
Gross Unrealized Losses	0
Investment securities available for sale	100,000	104,000
Total held to maturity
Amortized Cost	22,619,000
Gross Unrealized Losses	479,000
Fair Value	22,140,000
State and municipal
Total available for sale
Amortized Cost	360,779,000	291,730,000
Gross Unrealized Gains	8,443,000	14,241,000
Gross Unrealized Losses	5,564,000	60,000
Investment securities available for sale	363,658,000	305,911,000
Total held to maturity
Amortized Cost	224,811,000	219,767,000
Gross Unrealized Gains	3,136,000	6,982,000
Gross Unrealized Losses	1,796,000	15,000
Fair Value	226,151,000	226,734,000
U.S. Government-sponsored mortgage-backed securities
Total available for sale
Amortized Cost	313,459,000	342,550,000
Gross Unrealized Gains	1,904,000	4,234,000
Gross Unrealized Losses	3,071,000	518,000
Investment securities available for sale	312,292,000	346,266,000
Total held to maturity
Amortized Cost	360,213,000	398,832,000
Gross Unrealized Gains	4,956,000	7,601,000
Gross Unrealized Losses	1,527,000	787,000
Fair Value	363,642,000	405,646,000
Corporate obligations
Total available for sale
Amortized Cost	31,000	31,000
Gross Unrealized Gains
Gross Unrealized Losses
Investment securities available for sale	31,000	31,000
Equity securities
Total available for sale
Amortized Cost	21,820,000	3,912,000
Gross Unrealized Gains
Gross Unrealized Losses	1,039,000
Investment securities available for sale	20,781,000	3,912,000
Total held to maturity
Gross Unrealized Losses	$ 0
Certificates of deposit
Total available for sale
Amortized Cost		2,176,000
Investment securities available for sale		$ 2,176,000