Summary of Significant Accounting Policies Accounts Receivable (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 95,958	$ 113,148
Revenues from contracts with customers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	89,727	107,804
Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable	$ 6,231	$ 5,344