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Summary of Significant Accounting Policies - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2018
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Jan. 01, 2018
Property, Plant and Equipment [Line Items]              
Percentage of investments in subsidiaries       100.00%      
Asset impairment charges $ 12,100 $ 18,400 $ 1,300 $ 12,087 $ 19,714 $ 58,476  
Minimum percentage of likelihood of realization of tax benefits (greater than)       50.00%      
Reclassification pursuant to change in accounting principle         0    
Accounting Standards Update 2016-01 | Cumulative Other Comprehensive Loss              
Property, Plant and Equipment [Line Items]              
Reclassification pursuant to change in accounting principle         (1,902)   $ (1,900)
Accounting Standards Update 2016-01 | Retained Earnings              
Property, Plant and Equipment [Line Items]              
Reclassification pursuant to change in accounting principle         $ 1,902   $ 1,900
Buildings and improvements | Maximum              
Property, Plant and Equipment [Line Items]              
Estimated useful life       40 years      
Personal property | Maximum              
Property, Plant and Equipment [Line Items]              
Estimated useful life       12 years