Income Taxes - Reconciliation of Statutory Rate to Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory rate:	35.00%	35.00%	35.00%
State & local taxes-net of federal benefit	3.40%	2.80%	3.60%
Deferred tax revaluation-tax law change	(17.30%)	0.00%	0.00%
Amortization of investment tax credit	(0.20%)	(0.30%)	(0.20%)
Domestic production deduction	(1.40%)	(0.40%)	(1.00%)
Energy efficiency building deductions	(0.00%)	(1.70%)	(2.30%)
Research and development credit	(0.30%)	(0.60%)	(1.60%)
Other tax credits	(0.10%)	(0.10%)	(0.10%)
All other-net	(1.40%)	0.10%	0.20%
Effective tax rate	17.70%	34.80%	33.60%