Leases (Summary of Lease Assets and Liabilities) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Leases [Abstract]
Operating lease asset	$ 122,322	$ 146,522
Finance lease asset	12,630	13,179
Total lease assets	134,952	159,701
Operating lease liability, current	29,671	28,813
Finance lease liability, current	3,532	3,622
Total lease liabilities, current	33,203	32,435
Operating lease liability, noncurrent	129,658	166,452
Finance lease liability, noncurrent	25,739	27,872
Total lease liabilities, noncurrent	155,397	194,324
Total lease liabilities	$ 188,600	$ 226,759
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Property and equipment, net of accumulated depreciation of $272,532 and $261,082	Property and equipment, net of accumulated depreciation of $272,532 and $261,082
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]