Summary of Significant Accounting Policies - Options and Common Stock (Details) - shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Stock Held in Treasury, at Cost
Number of shares of common stock held in treasury	19,200,000	18,000,000
Stock options
Share-based compensation
Options granted (in shares)	0	0	0