Annual report pursuant to Section 13 and 15(d)

Derivative Financial Instruments - Classifications on Consolidated Balance Sheets (Details)

v3.8.0.1
Derivative Financial Instruments - Classifications on Consolidated Balance Sheets (Details) - Designated as Hedging Instrument [Member]
 1 Months Ended 12 Months Ended
Dec. 31, 2017
USD ($)
swaps
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Derivatives, Fair Value [Line Items]      
Notional Amount $ 475,000,000 $ 475,000,000  
Fair Value 5,345,000 5,345,000 $ 3,993,000
Interest Rate Swap One [Member]      
Derivatives, Fair Value [Line Items]      
Notional Amount $ 150,000,000 $ 150,000,000  
Company Fixed Pay Rate 1.30% 1.30%  
Fair Value $ 326,000 $ 326,000 (344,000)
Interest Rate Swap Two [Member]      
Derivatives, Fair Value [Line Items]      
Notional Amount $ 175,000,000 $ 175,000,000  
Company Fixed Pay Rate 1.03% 1.03%  
Fair Value $ 5,207,000 $ 5,207,000 4,337,000
Interest Rate Swap Three [Member]      
Derivatives, Fair Value [Line Items]      
Notional Amount $ 150,000,000 $ 150,000,000  
Company Fixed Pay Rate 2.20% 2.20%  
Fair Value $ (188,000) $ (188,000) $ 0
Number of swaps entered into | swaps 3    
London Interbank Offered Rate (LIBOR) [Member] | Interest Rate Swap One [Member]      
Derivatives, Fair Value [Line Items]      
Interest Rate Term   1 month  
London Interbank Offered Rate (LIBOR) [Member] | Interest Rate Swap Two [Member]      
Derivatives, Fair Value [Line Items]      
Interest Rate Term   1 month  
London Interbank Offered Rate (LIBOR) [Member] | Interest Rate Swap Three [Member]      
Derivatives, Fair Value [Line Items]      
Interest Rate Term   1 month