Long-Term Obligations (Details) - Revolving credit facility
$ in Millions
6 Months Ended
Jun. 30, 2017
USD ($)
Long-Term Obligations  
Outstanding borrowings $ 0.0
Commitment fee for quarterly unused capacity (as a percent) 0.25%
Unused line of credit fee threshold $ 15.0
Prime Rate  
Long-Term Obligations  
Variable interest rate basis Prime Rate
LIBOR  
Long-Term Obligations  
Variable interest rate basis LIBOR
2016 Loan Agreement  
Long-Term Obligations  
Maximum borrowing capacity $ 30.0
Minimum | Prime Rate  
Long-Term Obligations  
Basis spread on variable rate (as a percent) 0.00%
Minimum | LIBOR  
Long-Term Obligations  
Basis spread on variable rate (as a percent) 2.50%
Maximum | Prime Rate  
Long-Term Obligations  
Basis spread on variable rate (as a percent) 0.25%
Maximum | LIBOR  
Long-Term Obligations  
Basis spread on variable rate (as a percent) 2.75%