Balance Sheet Account Detail

(a) Property and Equipment

Property and equipment consisted of the following:



	March 31, 2016			December 31, 2015
Production equipment, molds, and office furniture	$	15,017		$	13,603
Computer hardware and software	7,363			6,380
Leasehold improvements	15,452			14,345
Construction in progress (software and related implementation, production equipment, and leasehold improvements)	899			510
Property and equipment, at cost	$	38,731		$	34,838
Accumulated depreciation	(12,783		)	(11,483		)
Property and equipment, net	$	25,948		$	23,355

Depreciation expense for property and equipment for the three months ended March 31, 2016 and 2015 was $1.3 million and $1.1 million, respectively.

(b) Inventories

Inventories consisted of the following:



	March 31, 2016		December 31, 2015
Raw materials	$	7,656	$	7,701
Work-in-process	13,270		4,355
Finished goods	22,363		15,804
Total Inventories	$	43,289	$	27,860

The following table presents goodwill, indefinite lived intangible assets, finite lived intangible assets and related accumulated amortization:



	March 31, 2016			December 31, 2015
Goodwill (1)	$	93,731		$	28,685

Intangible assets:
Indefinite lived intangibles
Trademarks and trade names	$	2,708		$	2,708
In-process research and development (1)	20,906			—

Finite lived intangibles
Developed technology (1)	$	81,912		$	40,100
Accumulated amortization	(1,471		)	(690		)
Developed technology, net	$	80,441		$	39,410

License	$	—		$	100
Accumulated amortization	—			(100		)
License, net	$	—		$	—

Customer relationships (1)	$	10,453		$	—
Accumulated amortization	(174		)	—
Customer relationships, net	$	10,279		$	—

Intangible assets (excluding goodwill), net	$	114,334		$	42,118

(1) Difference in the value between these dates is mainly due to acquisition of TriVascular. Refer to Note 12 of the condensed consolidated financial statements for further discussion.

Amortization expense for intangible assets for the three months ended March 31, 2016 and 2015 was $1.0 million and $0.4 million, respectively.

Estimated amortization expense for the five succeeding years and thereafter is as follows:



Remainder of 2016	$	4,077
2017	6,571
2018	8,067
2019	9,262
2020	10,573
2021 & Thereafter	52,170
Total	$	90,720

(d) Marketable securities

Investments in held-to-maturity marketable securities consist of the following at March 31, 2016 and December 31, 2015:



	March 31, 2016
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Agency bonds	$	8,000	$	—	$	(5	)	$	7,995
Commercial paper	2,497		—		—			2,497
Government securities	35,944		15		(2		)	35,957
Total	$	46,441	$	15	$	(7	)	$	46,449

	December 31, 2015
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Agency bonds	$	8,000	$	—	$	(20	)	$	7,980
Corporate bonds	40,824		1		(33		)	40,792
Commercial paper	3,944		—		—			3,944
Total	$	52,768	$	1	$	(53	)	$	52,716

At March 31, 2016, the Company’s investments included 3 held-to-maturity debt securities in unrealized loss positions with a total unrealized loss of approximately $7 thousand and a total fair market value of approximately $12.0 million. All investments with gross unrealized losses have been in unrealized loss positions for less than 6 months. The unrealized losses were caused by interest rate fluctuations. There was no change in the credit risk of the securities. The Company does not intend to sell the securities and it is not likely that the Company will be required to sell the securities before the expected recovery of their amortized cost bases. There were no realized gains or losses on the investments for the three months ended March 31, 2016. All of the Company's investments of held-to-maturity securities will mature within less than 12 months with an average maturity of 5 months.

(e) Fair Value Measurements

The following fair value hierarchy table presents information about each major category of the Company’s assets and liabilities measured at fair value on a recurring basis as of March 31, 2016 and December 31, 2015:



	Fair value measurement at reporting date using:
	Quoted prices in active markets for identical assets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)		Total
At March 31, 2016
Cash and cash equivalents	$	39,773	$	—	$	—	$	39,773
Contingently issuable common stock	$	—	$	—	$	14,700	$	14,700
Derivative liabilities	$	—	$	—	$	29,884	$	29,884
At December 31, 2015
Cash and cash equivalents	$	124,553	$	—	$	—	$	124,553
Contingently issuable common stock	$	—	$	—	$	14,700	$	14,700

There were no re-measurements to fair value during the three months ended March 31, 2016 of financial assets and liabilities that are not measured at fair value on a recurring basis. There were no transfers between Level 1, Level 2 or Level 3 securities during the three months ended March 31, 2016.

(f) Financial Instruments Not Recorded at Fair Value on a Recurring Basis

We measure the fair value of our Senior Notes carried at amortized cost quarterly for disclosure purposes. The estimated fair value of the Senior Notes is determined by Level 2 inputs and is based primarily on quoted market prices for the same or similar securities. Based on the market prices, the fair value of our long-term debt was $192.1 million as of March 31, 2016 and $207.9 million as of December 31, 2015.

We measure the fair value of our held-to-maturity marketable securities carried at amortized cost quarterly for disclosure purposes. The fair value of marketable securities is determined by Level 2 inputs and is based primarily on quoted market prices for the same or similar instruments.