INTANGIBLE ASSETS

Our intangible assets are as follows:



(in thousands)	June 30, 2018			December 31, 2017
Definite-lived intangible assets
Customer relationships	$	24,876		$	25,494
Unpatented technology	12,454			12,910
Patented technology	6,546			6,542
Tradename	12,650			13,951
Backlog	17,760			18,060
All other	8,641			7,611
Gross value of definite-lived intangible assets	82,927			84,568
Customer relationships amortization	(13,643		)	(12,455		)
Unpatented technology amortization	(3,002		)	(2,184		)
Patented technology amortization	(2,309		)	(2,213		)
Tradename amortization	(3,372		)	(3,042		)
Acquired backlog amortization	(17,760		)	(16,622		)
All other amortization	(7,778		)	(7,292		)
Accumulated amortization	(47,864		)	(43,808		)
Net definite-lived intangible assets	$	35,063		$	40,760

Indefinite-lived intangible assets:
Trademarks and trade names	$	1,305		$	1,305
Total indefinite-lived intangible assets	$	1,305		$	1,305

The following summarizes the changes in the carrying amount of intangible assets:



	Six months ended June 30,
(in thousands)	2018			2017
Balance at beginning of period	$	42,065		$	65,496
Amortization expense	(4,056		)	(6,334		)
Currency translation adjustments and other	(1,641		)	(14,088		)
Balance at end of the period	$	36,368		$	45,074

Amortization of intangible assets is included in cost of operations and SG&A in our condensed consolidated statement of operations but it is not allocated to segment results.

Estimated future intangible asset amortization expense is as follows (in thousands):



Year ending	Amortization expense
Three months ending September 30, 2018	$	1,311
Three months ending December 31, 2018	$	1,311
Twelve months ending December 31, 2019	$	4,763
Twelve months ending December 31, 2020	$	4,002
Twelve months ending December 31, 2021	$	3,772
Twelve months ending December 31, 2022	$	3,685
Twelve months ending December 31, 2023	$	3,677
Thereafter	$	12,542