Summary of Significant Accounting Policies (Additional Disclosures) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 Filinggroup	Dec. 31, 2015 USD ($) Filinggroup	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Accounting Policies [Line Items]
Lost-in-hole revenue | $		$ 3.8	$ 4.7	$ 5.9
Number of U.S. tax return filing groups		2
Forecast [Member]
Accounting Policies [Line Items]
Number of U.S. tax return filing groups	1