Pension Plan (Details) - Weighted average asset allocations by asset category	Dec. 31, 2016	Dec. 31, 2015
Pension Plan (Details) - Weighted average asset allocations by asset category [Line Items]
Total pension plan assets	100.00%	100.00%
Equity And Index Funds [Member]
Pension Plan (Details) - Weighted average asset allocations by asset category [Line Items]
Total pension plan assets	68.90%	68.50%
Fixed Income Funds [Member]
Pension Plan (Details) - Weighted average asset allocations by asset category [Line Items]
Total pension plan assets	31.10%	31.50%