Lease Commitments - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) renewal_term	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Operating Leased Assets [Line Items]
Rent expense	$ 43.8	$ 16.9	$ 16.1
Rent income	$ 7.2	$ 6.3	$ 6.0
Towers [Member]
Operating Leased Assets [Line Items]
Number of renewals | renewal_term	4
Term of renewals	5 years
Towers [Member] | Minimum [Member]
Operating Leased Assets [Line Items]
Terms of leases	5 years
Towers [Member] | Maximum [Member]
Operating Leased Assets [Line Items]
Terms of leases	10 years
Other [Member] | Minimum [Member]
Operating Leased Assets [Line Items]
Terms of leases	5 years
Other [Member] | Maximum [Member]
Operating Leased Assets [Line Items]
Terms of leases	20 years