Employee Benefit Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2010
Defined Benefit Plan Disclosure
Defined Benefit Plan, Description of Direction and Pattern of Change for Assumed Health Care Cost Trend Rate	0.065
Pension benefits to be amortized from accumulated other comprehensive income (loss) into net periodic cost over the next fiscal year	$ 99,000
Ultimate Health Care Cost Trend Rate	4.00%
Time Period of Lower Returns on Equity Securites	10 years
Cash and Cash Equivalents	$ 71,115,000	$ 61,454,000	$ 53,820,000	$ 62,542,000
Defined Contribution Plan, Employer Discretionary Contribution Amount	1,454,000	1,048,000	924,000
Pension benefits
Defined Benefit Plan Disclosure
Cash and Cash Equivalents	352,000	373,000
Accrued Investment Income Receivable	1,000	2,000
Components of net periodic benefit costs:
Interest cost	447,000	509,000	543,000
Expected return on plan assets	(493,000)	(589,000)	(659,000)
Amortization of net loss (gain)	117,000	137,000	189,000
Settlement of benefit obligation	459,000	1,400,000	270,000
Net periodic benefit cost	$ 530,000	$ 1,457,000	$ 343,000
Discount rate	3.80%	3.70%	3.75%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.50%	7.50%	7.50%
Postretirement benefits
Components of net periodic benefit costs:
Interest cost	$ 4,000	$ 6,000	$ 5,000
Expected return on plan assets	0	0	0
Amortization of net loss (gain)	(5,000)	(8,000)	(7,000)
Settlement of benefit obligation	0	0	0
Net periodic benefit cost	$ (1,000)	$ (2,000)	$ (2,000)
Discount rate	3.50%	4.30%	3.30%
Postretirement benefits | Employees hired before January 1, 2003
Defined Benefit Plan Disclosure
Contribution per eligible employee, coverage basis, consecutive period of highest average monthly compensation	5 years
Contribution per eligible employee, coverage basis, lastest service period	10 years
Postretirement benefits | Employees hired on or after January 1, 2003
Defined Benefit Plan Disclosure
Percentage of annual contribution per eligible employee	2.00%
Postretirement health benefits | Employees retired before January 1, 1993
Defined Benefit Plan Disclosure
Maximum coverage per eligible retiree	100.00%
Minimum
Defined Benefit Plan Disclosure
Defined Contribution Plan, Employer Matching Contribution, Percent	0.00%
Defined Contribution Plan, Maximum Annual Contribution Per Employee, Percent	3.00%
Minimum | Equity securities
Defined Benefit Plan Disclosure
Actual Plan Asset Allocations	60.00%
Minimum | Investment securities
Defined Benefit Plan Disclosure
Actual Plan Asset Allocations	2000.00%
Maximum
Defined Benefit Plan Disclosure
Defined Contribution Plan, Maximum Annual Contribution Per Employee, Percent	5.00%
Maximum | Equity securities
Defined Benefit Plan Disclosure
Actual Plan Asset Allocations	75.00%
Maximum | Investment securities
Defined Benefit Plan Disclosure
Actual Plan Asset Allocations	43.00%