INTANGIBLE ASSETS

Our intangible assets are as follows:



(in thousands)	September 30, 2017			December 31, 2016
Definite-lived intangible assets
Customer relationships	$	59,683		$	47,892
Unpatented technology	19,941			18,461
Patented technology	6,560			2,499
Tradename	22,818			18,774
Backlog	30,088			28,170
All other	7,550			7,429
Gross value of definite-lived intangible assets	146,640			123,225
Customer relationships amortization	(21,931		)	(17,519		)
Unpatented technology amortization	(4,443		)	(2,864		)
Patented technology amortization	(2,043		)	(1,532		)
Tradename amortization	(4,749		)	(3,826		)
Acquired backlog amortization	(27,814		)	(21,776		)
All other amortization	(6,965		)	(5,974		)
Accumulated amortization	(67,945		)	(53,491		)
Net definite-lived intangible assets	$	78,695		$	69,734

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:



	Nine months ended September 30,
(in thousands)	2017			2016
Balance at beginning of period	$	71,039		$	37,844
Business acquisitions	19,500			55,438
Amortization expense	(14,455		)	(11,904		)
Currency translation adjustments and other	3,916			647
Balance at end of the period	$	80,000		$	82,025

The January 11, 2017 acquisition of Universal resulted in an increase in our intangible asset amortization expense during the three and nine months ended September 30, 2017 of $0.5 million and $2.6 million, respectively.

The July 1, 2016 acquisition of SPIG, S.p.A. resulted in an increase in our intangible asset amortization expense during the three and nine months ended September 30, 2017 of $1.9 million and $7.3 million, respectively, and $7.1 million of intangible asset amortization expense during the three months ended September 30, 2016.

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

Estimated future intangible asset amortization expense, including the increase in amortization expense resulting from the January 11, 2017 acquisition of Universal, is as follows (in thousands):



Period ending	Amortization expense
Three months ending December 31, 2017	$	3,582
Twelve months ending December 31, 2018	$	12,444
Twelve months ending December 31, 2019	$	10,342
Twelve months ending December 31, 2020	$	9,042
Twelve months ending December 31, 2021	$	8,782
Twelve months ending December 31, 2022	$	7,205
Thereafter	$	27,298