Leases (Summary of Lease Assets and Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases [Abstract]
Operating lease asset	$ 133,044	$ 146,522
Finance lease asset	12,355	13,179
Total lease assets	145,399	159,701
Operating lease liability, current	33,771	28,813
Finance lease liability, current	3,612	3,622
Total lease liabilities, current	37,383	32,435
Operating lease liability, noncurrent	135,381	166,452
Finance lease liability, noncurrent	24,617	27,872
Total lease liabilities, noncurrent	159,998	194,324
Total lease liabilities	$ 197,381	$ 226,759
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Property and equipment, net of accumulated depreciation of $284,351 and $261,082	Property and equipment, net of accumulated depreciation of $284,351 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]