Leases - Operating and Finance Lease Right-of-use-assets and Related Lease Obligations (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases
Operating lease assets	$ 8,106	$ 4,542
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Operating lease assets
Finance lease assets	$ 19,563	20,544
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Finance lease assets
Total leased assets	$ 27,669	25,086
Operating liabilities current	$ 3,874	$ 2,573
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current	Other Liabilities, Current
Finance liabilities current	$ 921	$ 756
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current
Operating liabilities noncurrent	$ 4,220	$ 1,949
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other Liabilities, Noncurrent	Other Liabilities, Noncurrent
Finance liabilities noncurrent	$ 46,672	$ 47,393
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Finance liabilities noncurrent
Total lease liabilities	$ 55,687	52,671
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent us-gaap:OtherLiabilitiesNoncurrent
Finance lease, accumulated depreciation	$ 49,200	48,400
Prepaid financing costs	$ 700	$ 700