Leased Assets and Liabilities (Operating and Finance Lease Assets and Liabilities) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating	$ 180,983	$ 156,788
Finance	11,501	10,683
Total leased assets	192,484	167,471
Current operating lease liabilities	34,612	37,208
Noncurrent operating lease liabilities	154,648	127,237
Accounts payable and accrued liabilities	2,809	2,708
Other noncurrent liabilities	7,739	7,054
Total lease liabilities	$ 199,808	$ 174,207
Maximum
Lessee, Lease, Description [Line Items]
Term of contract	15 years
Option to extend	5 years