Stock-Based Compensation Stock-Based Compensation (Activity Pertaining to Nonemployee Director Stock Award Plan) (Details) - Directors Plan - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, beginning balance	150,500	171,500	192,500
Weighted average price, beginning balance	$ 54.18	$ 51.70	$ 49.39
Number of shares, granted	0	0	0
Weighted average price, granted	$ 0.00	$ 0.00	$ 0.00
Number of shares, exercised	0	(21,000)	(17,500)
Weighted average price, exercised	$ 0.00	$ 33.94	$ 32.53
Number of shares, forfeited	(21,000)	0	(3,500)
Weighted average price, forfeited	$ 54.35	$ 0.00	$ 20.46
Number of shares, ending balance	129,500	150,500	171,500
Weighted average price, ending balance	$ 54.15	$ 54.18	$ 51.70