20. Intangible assets



As at December 31, 2017		Cost		Accumulated amortization		Net book value
Trade names and trademarks	$	53,566	$	(461)	$	53,105
Customer relationships		125,234		(9,487)		115,747
Software		110,201		(26,898)		83,303
Software under development		8,939		-		8,939
	$	297,940	$	(36,846)	$	261,094

20. Intangible assets (continued)



As at December 31, 2016		Cost		Accumulated amortization		Net book value
Trade names and trademarks	$	5,585	$	(50)	$	5,535
Customer relationships		25,618		(1,072)		24,546
Software		36,566		(13,116)		23,450
Software under development		18,773		-		18,773
	$	86,542	$	(14,238)	$	72,304

During the year ended December 31, 2017, the Company recognized an impairment loss of $8,911,000 due to the impairment of certain software and software under development (2016: the Company recorded an impairment loss on the Equipment One customer relationships of $4,669,000; 2015: nil) (note 7).

At December 31, 2017, a net carrying amount of $59,380,000 (December 31, 2016: $22,665,000) included in intangible assets was not subject to amortization. During the year ended December 31, 2017, the cost of additions was reduced by $888,000 for recognition of tax credits (2016: $1,094,000; 2015: $1,678,000)

During the year ended December 31, 2017, interest of $281,000 (2016: $356,000; 2015: $772,000) was capitalized to the cost of software under development. These interest costs relating to qualifying assets are capitalized at a weighted average rate of 3.18% (2016: 4.91%; 2015: 6.39%).

During the year ended December 31, 2017, the weighted average amortization period for all classes of intangible assets was 7.9 years (2016: 8.2 years; 2015: 7.9 years).

As at December 31, 2017, estimated annual amortization expense for the next five years ended December 31 are as follows:



2018	$	31,463
2019		29,535
2020		24,141
2021		21,285
2022		19,024
	$	125,448