Lease Commitments - Lease Cost (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 10,617
Amortization of finance lease assets	55
Interest on finance lease liabilities	2
Total finance lease cost	57
Net lease cost	10,674
Short-term lease, cost	1,886
Variable lease, cost	836
Cost of Sales
Lessee, Lease, Description [Line Items]
Operating lease cost	9,235
Selling, General and Administrative Expenses
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 1,382