Leases - Operating and Finance Lease Right-of-use-assets and Related Lease Obligations (Details) $ in Thousands	Mar. 31, 2019 USD ($)
Leases
Operating lease assets	$ 7,453
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Operating lease assets
Finance lease assets	$ 22,895
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Finance lease assets
Total leased assets	$ 30,348
Operating liabilities current	$ 3,646
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other Liabilities, Current
Operating liabilities noncurrent	$ 3,805
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other Liabilities, Noncurrent
Finance liabilities noncurrent	$ 48,549
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Finance liabilities noncurrent
Total lease liabilities	$ 56,000
Finance lease, accumulated depreciation	46,700
Prepaid financing costs	$ 800