Business and Summary of Significant Accounting Principles (Asset Retirement Obligation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, beginning	$ 35,060	$ 31,940
Liability incurred	1,580	2,048
Revisions in estimated cash flows, including adjustment from tower transaction (Note 2)	3,368
Accretion expense	1,229	1,121	$ 1,249
Liability settled	(82)	(49)
Balance, ending	$ 41,155	$ 35,060	$ 31,940