Asset Retirement Obligation
 6 Months Ended
Jun. 30, 2018
Asset Retirement Obligation [Abstract]  
Asset Retirement Obligation
Asset Retirement Obligation
The Company's asset retirement obligations represent the estimated cost of decommissioning the turbines, removing above-ground installations and restoring the sites at the end of its estimated economic useful life.
The following table presents a reconciliation of the beginning and ending aggregate carrying amounts of asset retirement obligation (in thousands):
 
 
Six months ended June 30,
 
 
2018
 
2017
Beginning asset retirement obligations
 
$
56,619

 
$
44,783

Net additions during the period (1)
 
41,478

 
5,994

Foreign currency translation adjustment
 
(1,926
)
 
91

Reclassification to liabilities held for sale
 
(2,529
)
 
—

Accretion expense
 
1,781

 
1,357

Ending asset retirement obligations
 
$
95,423

 
$
52,225


(1)        Reflects additions due to the Japan Acquisition. See Note 5, Acquisitions, for discussion of the acquisition.