Stockholders' Equity Stockholders' Equity Mandatory Convertible Preferred Stock (Details) - $ / shares		9 Months Ended	12 Months Ended
	Jul. 18, 2018	Sep. 30, 2018	Dec. 31, 2017	Jun. 30, 2018	Jan. 01, 2018	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		1,600,000	1,600,000	2,000,000	2,000,000	2,000,000	2,000,000	2,000,000
9.75% Preferred Share Dividend Rate, Series A Mandatory Convertible, $1,000 per share liquidation preference		9.75%	9.75%
Preferred Stock, Liquidation Preference Per Share		$ 1,000	$ 1,000
9.75% Series A Mandatory Convertible, $1,000 per share liquidation preference
Class of Stock [Line Items]
Preferred stock, shares outstanding (in shares)		1,600,000
9.75% Preferred Share Dividend Rate, Series A Mandatory Convertible, $1,000 per share liquidation preference		9.75%
Preferred Stock, Liquidation Preference Per Share		$ 1,000
Preferred Stock, Dividends Per Share, Declared	$ 24.375
Depositary Stock, Dividends Per Share, Declared	$ 1.21875