Carryforwards (Details 4) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
State and local jurisdiction [Member]
Carryforwards [Line Items]
Operating loss carryforwards	$ 114.7	$ 116.2
Investment tax credit carryforward, amount	20.7	13.9
Federal and State Taxing Authority [Member]
Carryforwards [Line Items]
Tax credit carryforward, amount	$ 43.3	$ 21.3