19. Intangible assets



As at December 31, 2018		Cost		Accumulated amortization		Net book value
Trade names and trademarks	$	53,409	$	(1,201)	$	52,208
Customer relationships		124,986		(22,010)		102,976
Software		127,320		(48,522)		78,798
Software under development		11,640		-		11,640
	$	317,355	$	(71,733)	$	245,622

19. Intangible assets (continued)



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

During the year ended December 31, 2018, the Company recognized an impairment loss of nil (2017: the Company recorded an impairment loss relating to certain software and software under development $8,911,000; 2016: the Company recorded an impairment loss on the Equipment One customer relationships of $4,669,000) (note 7).

At December 31, 2018, a net carrying amount of $61,883,000 (December 31, 2017: $59,380,000) included in intangible assets was not subject to amortization. During the year ended December 31, 2018, the cost of additions was reduced by $1,606,000 for recognition of tax credits (2017: $888,000; 2016: $1,094,000)

During the year ended December 31, 2018, interest of $460,000 (2017: $281,000; 2016: $356,000) was capitalized to the cost of software under development. These interest costs relating to qualifying assets are capitalized at a weighted average rate of 4.09% (2017: 3.18%; 2016: 4.91%).

During the year ended December 31, 2018, the weighted average amortization period for all classes of intangible assets was 8.2 years (2017: 7.9 years; 2016: 8.2 years).

As at December 31, 2018, estimated annual amortization expense for the next five years ended December 31 are as follows:



2019	$	35,651
2020		28,801
2021		23,303
2022		20,727
2023		16,567
	$	125,049