Summary of Significant Accounting Policies - Share-based Compensation (Details) - Performance shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares awarded as a percentage of granted		130.20%	131.50%
Vesting period	3 years
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares awarded as a percentage of granted	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares awarded as a percentage of granted	200.00%