SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2015

Investments at December 31, 2015 and 2014 consist of the following (in thousands):



	Amortized		Unrealized					Aggregate Fair
Investment Classification	Cost		Gains		(Losses)			Market Value
December 31, 2015
Certificates of deposit	$	11,532	$	3	$	(14	)	$	11,521
Corporate bonds	233,848		—		(139		)	233,709
U.S. Government bonds	54,953		1		(16		)	54,938
	$	300,333	$	4	$	(169	)	$	300,168
December 31, 2014
Certificates of deposit	$	11,373	$	4	$	(13	)	$	11,364
Corporate bonds	228,799		14		(41		)	228,772
U.S. Government bonds	5,999		—		—			5,999
	$	246,171	$	18	$	(54	)	$	246,135

Assets and liabilities carried at fair value measured on a recurring basis

The following table provides the assets and liabilities carried at fair value measured on a recurring basis as of December 31, 2015 (in thousands):



			Fair Value Measurements, Using
	Total carrying value as of December 31, 2015		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	34,980	$	34,980	$	—	$	—
Short-term investments	297,981		297,981		—		—
Long-term investments	2,187		2,187		—		—

The following table provides the assets and liabilities carried at fair value measured on a recurring basis as of December 31, 2014 (in thousands):



			Fair Value Measurements, Using
	Total carrying value as of December 31, 2014		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Cash equivalents	$	970	$	970	$	—	$	—
Short-term investments	243,088		243,088		—		—
Long-term investments	3,047		3,047		—		—

Reconciliation of the changes in fair value of the Company's investments in convertible notes

The following table is a reconciliation of the changes in fair value of the Company’s investments in convertible notes for the years ended December 31, 2015 and 2014, which had been classified in Level 3 in the fair value hierarchy (in thousands):



	Year Ended December 31,
	2015		2014
Fair value of notes, beginning of year	$	—	$	4,300
Repayments of notes	—		(4,300		)
Fair value of notes, end of year	$	—	$	—

Basic and diluted net income (loss) per common share

The following table is a reconciliation of net income and the shares used in calculating basic and diluted net income per common share for the years ended December 31, 2015, 2014 and 2013 (in thousands, except share and per share data):



	Year Ended December 31,
	2015		2014		2013
Numerator:
Net income	$	14,678	$	41,854	$	74,052
Denominator:
Weighted average common shares outstanding – Basic	46,816,394		46,252,960		45,898,019
Effect of dilutive shares:
Common stock equivalents arising from stock options and ESPP	267,145		265,129		458,574
Restricted stock units and performance units	410,649		167,056		187,012
Weighted average common shares outstanding – Diluted	47,494,188		46,685,145		46,543,605
Net income per common share:
Basic	$	0.31	$	0.90	$	1.61
Diluted	$	0.31	$	0.90	$	1.59

Research and development expenses

Research and development expenses consist of the following (in thousands):



	Year Ended December 31,
	2015		2014		2013
Development and operations in the Company’s facilities	$	34,348	$	27,891	$	23,491
PPG OLED Materials Agreement (Note 8)	7,912		10,614		7,470
Costs incurred under sponsored research agreements	1,795		2,014		2,671
Scientific Advisory Board compensation	586		635		583
	$	44,641	$	41,154	$	34,215

Non-cash activities

The following non-cash activities occurred (in thousands):



	Year Ended December 31,
	2015			2014			2013
Unrealized loss on available-for-sale securities	$	(129	)	$	(7	)	$	(10	)
Common stock issued to Board of Directors and Scientific Advisory Board that was earned in a previous period	300			323			315
Common stock issued to employees that was accrued for in a previous period	967			749			282
Property and equipment purchases included in accounts payable	467			965			420