Quarterly report pursuant to Section 13 or 15(d)

Basis of presentation (Details)

v3.10.0.1
Basis of presentation (Details)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
segment
Sep. 30, 2017
USD ($)
Interim Consolidated Financial Information        
Number of operating segments | segment     2  
Other Nonoperating Income (Expense) $ (12) $ (203) $ (479) $ (669)
Income Tax Expense (Benefit) $ 1,148 5,754 $ 6,802 10,668
Accounting Standards Updates 2017-07 [Member]        
Interim Consolidated Financial Information        
Other Nonoperating Income (Expense)   $ 179   $ 537