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Income Taxes (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Operating Loss Carryforwards [Line Items]      
Federal tax rate, percent 21.00%   35.00%
Income tax benefit from the Tax Act     $ 39,300
Income tax provision $ 20,633 $ 26,846  
Effective income tax rates 27.60% 37.80%  
Actual income tax rates 27.00% 33.60%  
Unrecognized income tax benefits $ 800   800
Accrued interest expense related to unrecognized income tax benefits 100   100
Interest income related to unrecognized income tax benefits   $ 400  
Interest expense related to unrecognized income tax benefits 100    
Unrecognized tax benefits, decrease resulting from settlements with taxing authorities   $ 3,300  
Other Long-term Liabilities [Member]      
Operating Loss Carryforwards [Line Items]      
Income tax reserves $ 900   $ 900