Stock-Based Compensation - Long-Term Performance-Based Plans (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2013
2019 LTIP
Share-based compensation additional disclosures
Percentage of performance goals probable of achievement	82.00%
LTIP 2008
Share-based compensation additional disclosures
Portion meeting vesting condition (as a percent)						100.00%
LTIP 2013
Share-based compensation additional disclosures
Portion meeting vesting condition (as a percent)	20.00%
Percentage of performance goals probable of achievement			30.00%	10.00%	20.00%
LTIP 2017
Share-based compensation additional disclosures
Percentage of performance goals probable of achievement	75.00%	75.00%