Annual report pursuant to Section 13 and 15(d)

Basis of Presentation and Summary of Significant Accounting Policies - New Accounting Pronouncements (Details)

v3.8.0.1
Basis of Presentation and Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($)
3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Item Effected [Line Items]                      
Goodwill, Impairment Loss $ 89,000,000 $ 0 $ 0 $ 78,000,000 $ 64,000,000 $ 0 $ 0 $ 0 $ 167,000,000 $ 64,000,000 $ 0
Other non-current assets 9,118,000       7,233,000       9,118,000 7,233,000  
Long-term debt $ 598,958,000       $ 468,231,000       $ 598,958,000 $ 468,231,000