Income Taxes - Carryforwards (Details) $ in Millions	Dec. 31, 2017 USD ($)
Alternative minimum tax credit
Net operating loss carryforward
Alternative minimum tax credit that can be carried forward	$ 2.6
Federal
Net operating loss carryforward
Net operating loss carryforward	34.5
Federal | 2030
Net operating loss carryforward
Net operating loss carryforward	10.6
Federal | 2031
Net operating loss carryforward
Net operating loss carryforward	8.6
Federal | 2032
Net operating loss carryforward
Net operating loss carryforward	15.3
State
Net operating loss carryforward
Net operating loss carryforward	74.1
State | 2021
Net operating loss carryforward
Net operating loss carryforward	$ 73.6