Commitments and Contingencies Commitments and Contingencies (Details)	9 Months Ended
	Sep. 30, 2017 USD ($)
Loss Contingencies [Line Items]
Total costs to remediate IRC Section 7702 issue	$ 10,700,000
Toll charges and fees to remediate IRC Section 7702 issue	10,400,000
Cost of claim and reserve liabilities to remediate IRC Section 7702 issue	300,000
Additional General Expenses to Remediate Section 7702 and 72(s) Issue	1,600,000
Minimum [Member]
Loss Contingencies [Line Items]
Cost Range to Remediate IRC Section 7702 Issue	5,600,000
Minimum [Member] | IRC Section 7702 remediation costs [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	750,000
Maximum [Member]
Loss Contingencies [Line Items]
Cost Range to Remediate IRC Section 7702 Issue	34,000,000
Maximum [Member] | IRC Section 7702 remediation costs [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	$ 1,250,000