Incentive Plans (Details) - shares shares in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Stock option [Roll Forward]
Total common shares reserved for issuance (in shares)	4,430
1993 Stock Incentive Plan [Member]
Stock option [Roll Forward]
Stock option grants (in shares)	0	0
Stock options exercisable (in shares)	0	0
Stock options outstanding (in shares)	0	0
Total common shares reserved for issuance (in shares)	4,320
Other Employee Benefit Plan [Member]
Stock option [Roll Forward]
Total common shares reserved for issuance (in shares)	110