Commitments and Contingencies

12 Months Ended

Dec. 31, 2015

9. Commitments and Contingencies

Operating Leases

We lease facilities and equipment under operating lease arrangements that have terms expiring at various dates through 2020. Certain lease arrangements include renewal options and escalation clauses. In addition, various lease agreements to which we are party require that we comply with certain customary covenants throughout the term of these leases. If we are unable to comply with these covenants and cannot reach a satisfactory resolution in the event of noncompliance, these agreements could terminate.

Future minimum lease payments under non-cancelable operating leases as of December 31, 2015 are as follows (in thousands):

Year Ending December 31,
2016	$	3,716
2017		3,447
2018		2,636
2019		498
2020		237
Thereafter		—

Total	$	10,534

Total rent expense was $3.8 million, $3.6 million and $3.5 million for the years ended December 31, 2015, 2014 and 2013, respectively.

Milestone Payments

We are party to certain license agreements as described in Note 15—Assignment and License Agreements and acquisition agreements. Generally, these agreements require that we make milestone payments in cash upon the achievement of certain product development and commercialization goals and payments of royalties upon commercial sales.

Future milestone payments based on our estimates of the timing and probability of achieving milestones specified under these arrangements are as follows (in thousands):

Year Ending December 31,	(1)
2016	$	6,136
2017		4,640
2018		3,705
2019		9,711
2020		1,759
Thereafter		7,070

Total	$	33,021


(1)	The amounts and timing of future milestone payments may vary depending on when related milestones will be attained, if at all.