Quarterly report pursuant to Section 13 or 15(d)

Income taxes (Details Textual)

v3.8.0.1
Income taxes (Details Textual) - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Percent 17.50%   14.70%    
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount   $ 2.9      
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Percent   21.00%      
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability         $ 0.0
Effective Income Tax Rate Reconciliation, Deduction, Dividend, Percent         100.00%
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount         $ 1.9
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent         35.00%
Scenario, Plan [Member]          
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent       21.00%  
Tax Year 2017 [Member]          
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent         10.50%
Tax Year 2025 [Member]          
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent         13.125%