6. Software and Other Intangible Assets

At September 30, 2014, software net book value totaling $207.7 million, net of $119.9 million of accumulated amortization, includes the net book value of software marketed for external sale of $88.8 million. The remaining software net book value of $118.9 million is comprised of various software that has been acquired or developed for internal use.

At December 31, 2013, software net book value totaled $191.5 million, net of $95.3 million of accumulated amortization. Included in this amount is software marketed for external sale of $94.0 million. The remaining software net book value of $97.5 million is comprised of various software that has been acquired or developed for internal use.

Quarterly amortization of software marketed for external sale is computed using the greater of the ratio of current revenues to total estimated revenues expected to be derived from the software or the straight-line method over an estimated useful life of three to ten years. Software for resale amortization expense recorded in the three months ended September 30, 2014 and 2013 totaled $3.8 million and $3.4 million, respectively. These software amortization expense amounts are reflected in cost of software license fees in the condensed consolidated statements of income. Software for resale amortization expense recorded in the nine months ended September 30, 2014 and 2013 totaled $10.9 million and $10.1 million, respectively. These software amortization expense amounts are reflected in cost of software license fees in the condensed consolidated statements of income.

Quarterly amortization of software for internal use is computed using the straight-line method over an estimated useful life of three to ten years. Software for internal use includes software acquired through acquisitions that is used to provide certain of our hosted offerings. Amortization of software for internal use of $7.7 million and $5.0 million for the three months ended September 30, 2014 and 2013, respectively, is included in depreciation and amortization in the condensed consolidated statements of income. Amortization of software for internal use of $18.9 million and $12.8 million for the nine months ended September 30, 2014 and 2013, respectively, is included in depreciation and amortization in the condensed consolidated statements of income.

The carrying amount and accumulated amortization of the Company’s other intangible assets that were subject to amortization at each balance sheet date are as follows:


	September 30, 2014							December 31, 2013
(in thousands)	Gross Carrying Amount		Accumulated Amortization			Net Balance		Gross Carrying Amount		Accumulated Amortization			Net Balance
Customer relationships	$	311,438	$	(64,368	)	$	247,070	$	277,356	$	(49,410	)	$	227,946
Trademarks and tradenames		15,671		(6,983	)		8,688		13,995		(4,383	)		9,612
Purchased Contracts		10,835		(10,835	)		—		10,865		(10,865	)		—
Covenant not to compete		438		(393	)		45		438		(303	)		135

	$	338,382	$	(82,579	)	$	255,803	$	302,654	$	(64,961	)	$	237,693

Other intangible assets amortization expense for the three months ended September 30, 2014 and 2013 totaled $6.1 million and $4.7 million, respectively. Other intangible assets amortization expense for the nine months ended September 30, 2014 and 2013 totaled $18.4 million and $13.3 million, respectively.

Based on capitalized software and other intangible assets at September 30, 2014, estimated amortization expense for future fiscal years is as follows:


Fiscal Year Ending December 31,	Software Amortization		Other Intangible Assets Amortization
(in thousands)
Remainder of 2014	$	11,335	$	5,960
2015		41,240		22,236
2016		36,133		21,099
2017		29,618		19,594
2018		24,134		19,084
2019		20,445		18,482
Thereafter		44,778		149,348

Total	$	207,683	$	255,803