Summary of Significant Accounting Policies (Schedule of Stock by Class) (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Common Class A [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding	60,909,831	60,552,673	60,794,114
Employee and non-employee director stock transactions	288,766	357,158	(241,441)
Share repurchases	(4,119,558)
Common Stock, Shares, Outstanding	57,079,039	60,909,831	60,552,673
Common Class B [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Shares, Outstanding	11,484,408	11,484,408	11,484,408
Employee and non-employee director stock transactions	0	0	0
Share repurchases	0
Common Stock, Shares, Outstanding	11,484,408	11,484,408	11,484,408