Debt (Debt Covenants and Compliance) (Details)	9 Months Ended
	Sep. 30, 2017 USD ($)
Debt Instrument [Line Items]
Total leverage ratio, covenant compliance	2.18
Senior secured leverage ratio to consolidated EBITDA	1.68
Ratio of interest coverage	7.19
Minimum [Member]
Debt Instrument [Line Items]
Ratio of interest coverage, covenant compliance	3.50
Maximum [Member]
Debt Instrument [Line Items]
Total leverage ratio, covenant compliance	3.75
Senior secured leverage ratio to consolidated EBITDA	3.50
Financing Agreement Senior Secured Credit Facility [Member]
Debt Instrument [Line Items]
Maximum annual dividend payment	$ 120,000,000
Financing Agreement Senior Secured Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Total leverage ratio	3.00
Senior secured leverage ratio	3.00
Total leverage ratio on unsecured debt	3.50