Income Taxes (Details) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2012	Dec. 31, 2015
Income Tax Examination [Line Items]
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	$ (200,000)		$ (1,100,000)		$ (400,000)
Interest Expense related to unrecognized tax benefits	900,000		(700,000)
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions	3,700,000		2,900,000
Unrecognized tax benefit — Temporary tax positions	6,200,000		16,800,000
Total unrecognized tax benefit	9,900,000		19,700,000
NOL and tax credit carryforwards	(3,900,000)		(5,800,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible	3,000,000
Amounts accrued for penalties related to unrecognized tax benefits	0		$ 0
Internal Revenue Service (IRS)
Tax Audits [Abstract]
Year(s) under examination		2012 and 2013		2010 and 2011
Year of carryback claim under examination				2009
Potential Tax Adjustments	$ 14,000,000
Earliest year subject to examination	2009
State Jurisdiction (Colorado)
Tax Audits [Abstract]
Earliest year subject to examination	2009