Lease Commitments - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Leased Assets [Line Items]
Lease Expiration Date	2033
Operating Leases, Rent Expense, Net	$ 83,636	$ 78,521	$ 77,405