Annual report pursuant to Section 13 and 15(d)

Postretirement Benefits, Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets (Details)

v3.6.0.2
Postretirement Benefits, Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets (Details) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets [Abstract]      
Projected benefit obligation $ 136,789 $ 128,829 $ 129,053
Accumulated benefit obligation 129,292 119,031  
Fair value of plan assets $ 89,643 $ 86,828 $ 84,893