Annual report pursuant to Section 13 and 15(d)

Fair Value Measurements - Schedule of Fair Value Measured On Recurring Basis (Details)

v3.8.0.1
Fair Value Measurements - Schedule of Fair Value Measured On Recurring Basis (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Fair value measurements    
Interest rate swap agreements - liabilities   $ (16,948)
Recurring    
Fair value measurements    
Interest rate swap agreements - assets $ 7,058 8,521
Interest rate swap agreements - liabilities (13,817) (16,948)
Total (6,759) (8,427)
Recurring | Level 1    
Fair value measurements    
Interest rate swap agreements - assets 0 0
Interest rate swap agreements - liabilities 0 0
Total 0 0
Recurring | Level 2    
Fair value measurements    
Interest rate swap agreements - assets 7,058 8,521
Interest rate swap agreements - liabilities (13,817) (16,948)
Total (6,759) (8,427)
Recurring | Level 3    
Fair value measurements    
Interest rate swap agreements - assets 0 0
Interest rate swap agreements - liabilities 0 0
Total $ 0 $ 0