Summary of Significant Accounting Policies and Other Items - Impairment of Long-Lived Assets and Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Asset impairment charges
Impairment charges of long-lived assets	$ 0	$ 0	$ 0
Impairment of goodwill	$ 0	$ 0	$ 0

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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration