v3.8.0.1
Interest Rate Swap (Details) - Designated as Hedging Instrument - Interest Rate Swap - Cash Flow Hedge - USD ($)
1 Months Ended
Apr. 30, 2017
Mar. 31, 2018
Derivative [Line Items]    
Fixed interest rate 1.78%  
Notional amount $ 500,000,000  
Reduction in notional amount per year $ 100,000,000  
Term of contract 5 years  
Effective fixed interest rate on long-term debt   4.03%
Other Assets    
Derivative [Line Items]    
Fair value of derivative   $ 6,600,000
LIBOR    
Derivative [Line Items]    
Basis spread on variable rate 0.75%