5. Balance Sheet Details

Property and Equipment, net. Property and equipment, net, consisted of the following (in thousands, except years):



	Useful Life	December 31,
	Useful Life	2013			2012
Instrument sets	3 to 4	$	171,454		$	159,960
Machinery and equipment	5 to 7	21,722			17,719
Computer equipment and software	3 to 7	46,896			37,690
Leasehold improvements	2 to 15	21,825			20,735
Furniture and fixtures	3 to 7	7,510			7,744
Building and improvements	10 to 20	7,371			7,195
Land	—	541			541
		277,319			251,584
Less: accumulated depreciation and amortization		(149,255		)	(126,461		)
		$	128,064		$	125,123

Depreciation expense was $43.8 million, $39.5 million, and $29.6 million for the years ended December 31, 2013, 2012 and 2011, respectively. At December 31, 2013 and 2012, assets recorded under capital leases of $1.8 million and $1.4 million, respectively, are included in the machinery and equipment balance. Amortization of assets under capital leases is included in depreciation expense.

Capitalized internal-use software costs include only those direct costs associated with the actual development or acquisition of computer software for internal use, including costs associated with the design, coding, installation, and testing of the system. At December 31, 2013 and 2012, the Company had $16.2 million and $14.6 million in unamortized capitalized software costs, respectively. Amortization expense related to capitalized internal-use software costs was $4.5 million, $2.8 million and $1.8 million for the years ended December 31, 2013, 2012 and 2011, respectively.

Goodwill and Intangible Assets. Goodwill and intangible assets as of December 31, 2013 consisted of the following (in thousands, except years):



	Weighted- Average Amortization Period (in years)	Gross Amount		Accumulated Amortization			Intangible Assets, net
Intangible Assets Subject to Amortization:
Purchased technology:
Developed technology	10	$	62,328	$	(21,359	)	$	40,969
Manufacturing know-how and trade secrets	12	21,997		(9,890		)	12,107
Trade name and trademarks	11	9,500		(3,317		)	6,183
Customer relationships	8	43,871		(19,784		)	24,087
	10	$	137,696	$	(54,350	)	$	83,346
Intangible Assets Not Subject to Amortization:
In-process research and development							10,640
Goodwill							154,944
Total goodwill and intangible assets, net							$	248,930

Goodwill and intangible assets as of December 31, 2012 consisted of the following (in thousands, except years):



	Weighted- Average Amortization Period (in years)	Gross Amount		Accumulated Amortization			Intangible Assets, net
Intangible Assets Subject to Amortization:
Purchased technology:
Developed technology	10	$	55,178	$	(14,966	)	$	40,212
Manufacturing know-how and trade secrets	12	21,712		(7,996		)	13,716
Trade name and trademarks	11	9,500		(2,333		)	7,167
Customer relationships	9	39,330		(9,703		)	29,627
	10	$	125,720	$	(34,998	)	$	90,722
Intangible Assets Not Subject to Amortization:
In-process research and development							10,640
Goodwill							154,106
Total goodwill and intangible assets, net							$	255,468

Total expense related to the amortization of intangible assets was $19.3 million, $12.4 million and $6.6 million for the years ended December 31, 2013, 2012 and 2011, respectively. In-process research and development will be amortized beginning on the approval date of the respective acquired products and will be amortized over the estimated useful life determined at that time.

Total future amortization expense related to intangible assets subject to amortization at December 31, 2013 is set forth in the table below (in thousands):



2014	$	14,343
2015	13,254
2016	12,776
2017	10,423
2018	9,905
Thereafter through 2026	22,645
Total future amortization expense	$	83,346

The changes to goodwill are comprised of the following (in thousands):



	December 31,
	2013		2012
Balance at beginning of period	$	154,106	$	159,349
Impairment charge	—		(8,300		)
Additions recorded in connection with business acquisitions	764		2,827
Other	74		230
Balance at end of period	$	154,944	$	154,106

Accounts Payable and Accrued Liabilities. Accounts payable and accrued liabilities consisted of the following (in thousands):



	December 31,
	2013		2012
Accounts payable	$	14,281	$	9,040
Accrued expenses	19,078		20,880
Royalties payable	38,967		19,861
Distributor commissions payable	7,319		7,523
Non-income taxes payable	3,951		3,144
Other	2,461		1,600
	$	86,057	$	62,048

Other Long-Term Liabilities. Other long-term liabilities consisted of the following (in thousands):



	December 31,
	2013		2012
Deferred rent	$	12,883	$	13,340
Capital lease obligation, non-current	223		426
Contingent consideration, non-current	596		1,074
Other	1,142		359
	$	14,844	$	15,199