Leased Assets and Liabilities (Operating and Finance Lease Assets and Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Operating	$ 152,139	$ 156,788
Finance	11,536	10,683
Total leased assets	163,675	167,471
Current operating lease liabilities	35,219	37,208
Noncurrent operating lease liabilities	124,873	127,237
Accounts payable and accrued liabilities	2,844	2,708
Other noncurrent liabilities	7,651	7,054
Total lease liabilities	$ 170,587	$ 174,207
Maximum
Lessee, Lease, Description [Line Items]
Term of contract	15 years
Option to extend	5 years