Income Taxes - Expiration of State NOL's and Gross Valuation Allowances (Details) - State and Local Jurisdiction $ in Thousands	Dec. 31, 2017 USD ($)
Net operating loss carry forwards
Net operating losses	$ 596,700
State Net Operating Losses
2018	1,812
2019	9,770
2020	10,483
2021	12,269
Thereafter through 2036	562,326
Gross Valuation Allowance
2018	1,081
2019	8,788
2020	8,333
2021	6,817
Thereafter through 2036	$ 426,138