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 6 Months Ended
Jun. 30, 2018
USD ($)
Jun. 30, 2017
USD ($)
Jun. 30, 2018
USD ($)
segment
Jun. 30, 2017
USD ($)
segment
Interim Consolidated Financial Information        
Number of operating segments | segment     2 2
Other Nonoperating Income (Expense) $ (264) $ (230) $ (467) $ (466)
Income Tax Expense (Benefit) $ 6,916 7,608 $ 5,654 4,914
Accounting Standards Updates 2017-07 [Member]        
Interim Consolidated Financial Information        
Other Nonoperating Income (Expense)   $ 179   $ 358