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Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Asset Retirement Obligation [Abstract]    
Asset Retirement Obligation, Beginning $ 11,334 $ 9,950
Liabilities Assumed in ATMI acquisition 0 589
Liabilities Settled (975) (698)
Liabilities Incurred 491 1,094
Accretion Expense 188 196
Revision of Estimate 491 203
Asset Retirement Obligation, Ending $ 11,529 $ 11,334