Income Taxes - Summary of Federal Net Operating Loss Carryforwards and Related Deferred Income Tax Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Deferred Tax Asset	$ 31.8	$ 52.2
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
NOL Carry-forwards	151.4
Deferred Tax Asset	31.8
Internal Revenue Service (IRS) [Member] | 2020 [Member]
Income Tax Contingency [Line Items]
NOL Carry-forwards	7.8
Deferred Tax Asset	1.6
Internal Revenue Service (IRS) [Member] | 2021 through 2025 [Member]
Income Tax Contingency [Line Items]
NOL Carry-forwards	30.5
Deferred Tax Asset	6.5
Internal Revenue Service (IRS) [Member] | 2026 through 2030 [Member]
Income Tax Contingency [Line Items]
NOL Carry-forwards	29.8
Deferred Tax Asset	6.2
Internal Revenue Service (IRS) [Member] | 2031 through 2037 [Member]
Income Tax Contingency [Line Items]
NOL Carry-forwards	83.3
Deferred Tax Asset	$ 17.5