Balance Sheet Account Detail

(a) Property and Equipment

Property and equipment consisted of the following:



	June 30, 2016			December 31, 2015
Production equipment, molds, and office furniture	$	14,430		$	13,603
Computer hardware and software	7,359			6,380
Leasehold improvements	15,495			14,345
Construction in progress (software and related implementation, production equipment, and leasehold improvements)	1,129			510
Property and equipment, at cost	$	38,413		$	34,838
Accumulated depreciation	(13,578		)	(11,483		)
Property and equipment, net	$	24,835		$	23,355

Depreciation expense for property and equipment for the three months ended June 30, 2016 and 2015 was $1.3 million and $1.1 million, respectively. For the six months ended June 30, 2016 and 2015 depreciation expense for property and equipment was $2.6 million and $2.2 million, respectively.

(b) Inventories

Inventories consisted of the following:



	June 30, 2016		December 31, 2015
Raw materials	$	9,072	$	7,701
Work-in-process	12,296		4,355
Finished goods	20,778		15,804
Total Inventories	$	42,146	$	27,860

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



	June 30, 2016			December 31, 2015
Goodwill (1)	$	120,693		$	28,685

Intangible assets:
Indefinite lived intangibles
Trademarks and trade names	$	2,708		$	2,708
In-process research and development (1)	11,200			—

Finite lived intangibles
Developed technology (1)	$	67,600		$	40,100
Accumulated amortization	(1,989		)	(690		)
Developed technology, net	$	65,611		$	39,410

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

Customer relationships (1)	$	7,500		$	—
Accumulated amortization	(313		)	—
Customer relationships, net	$	7,187		$	—

Intangible assets (excluding goodwill), net	$	86,706		$	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 June 30, 2016 and 2015 was $0.7 million and $0.4 million, respectively. For the six months ended June 30, 2016 and 2015 amortization expense for intangible assets was $1.6 million and $0.8 million, respectively.

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



Remainder of 2016	$	1,883
2017	4,978
2018	6,477
2019	7,674
2020	8,988
2021 & Thereafter	42,798
Total	$	72,798

(d) Marketable securities

Investments in held-to-maturity marketable securities consist of the following at June 30, 2016 and December 31, 2015:



	June 30, 2016
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Agency bonds	$	10,507	$	2	$	(1	)	10,508
Corporate bonds	2,510		—		(3		)	2,507
Commercial paper	2,500		—		—			2,500
Government securities	25,973		10		—			25,983
Total	$	41,490	$	12	$	(4	)	$	41,498

	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 June 30, 2016, the Company’s investments included 3 held-to-maturity debt securities in unrealized loss positions with a total unrealized loss of approximately $4 thousand and a total fair market value of approximately $10.5 million. All investments with gross unrealized losses have been in unrealized loss positions for less than 9 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 and six months ended June 30, 2016. All of the Company's investments of held-to-maturity securities will mature within less than 12 months with an average maturity of 4 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 June 30, 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 June 30, 2016
Cash and cash equivalents	$	31,448	$	—	$	—	$	31,448
Contingently issuable common stock	$	—	$	—	$	14,800	$	14,800
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 six months ended June 30, 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 six months ended June 30, 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 $244.2 million as of June 30, 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.