Summary of Significant Accounting Policies - Goodwill (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2019
Goodwill
Long-term growth rate used to calculate terminal values for each reporting unit (as a percent)		2.00%
Goodwill impairments	$ 93,634	$ 93,634

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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