4)	Investments

The fair value of investments classified as short-term consists of the following:

	September 30, 2018		December 31, 2017
Available-for-sale investments:
Time deposits and certificates of deposit	$	14,552	$	9,757
Bankers’ acceptance drafts		2,107		5,330
Asset-backed securities		38,947		36,990
Commercial paper		32,057		13,750
Corporate obligations		71,971		77,821
Municipal bonds		1,288		1,970
U.S. treasury obligations		28,208		28,078
U.S. agency obligations		30,646		35,738
	$	219,776	$	209,434

Investments classified as long-term consist of the following:

	September 30, 2018		December 31, 2017
Available-for-sale investments:
Group insurance contracts	$	6,004	$	6,255
Cost method investments:
Minority interest in a private company		4,400		4,400
	$	10,404	$	10,655

The following tables show the gross unrealized gains and (losses) aggregated by investment category for available-for-sale investments:

As of September 30, 2018:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
Short-term investments:
Available-for-sale investments:
Time deposits and certificates of deposit	$	14,552	$	—	$	—		$	14,552
Bankers’ acceptance drafts		2,107		—		—			2,107
Asset-backed securities		38,961		11		(25	)		38,947
Commercial paper		32,238		—		(181	)		32,057
Corporate obligations		71,931		59		(19	)		71,971
Municipal bonds		1,290		—		(2	)		1,288
U.S. treasury obligations		28,200		10		(2	)		28,208
U.S. agency obligations		30,649		4		(7	)		30,646
	$	219,928	$	84	$	(236	)	$	219,776

As of September 30, 2018:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
Long-term investments:
Available-for-sale investments:
Group insurance contracts	$	6,010	$	—	$	(6	)	$	6,004

As of December 31, 2017:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
Short-term investments:
Available-for-sale investments:
Time deposits and certificates of deposit	$	9,756	$	1	$	—		$	9,757
Bankers acceptance drafts		5,330		—		—			5,330
Asset-backed securities		37,017		15		(42	)		36,990
Commercial paper		13,810		—		(60	)		13,750
Corporate obligations		77,788		58		(25	)		77,821
Municipal bonds		1,970		—		—			1,970
U.S. treasury obligations		28,054		24		—			28,078
U.S. agency obligations		35,728		10		—			35,738
	$	209,453	$	108	$	(127	)	$	209,434

As of December 31, 2017:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)		Estimated Fair Value
Long-term investments:
Available-for-sale investments:
Group insurance contracts	$	6,006	$	249	$	—	$	6,255

The tables above, which show the gross unrealized gains and (losses) aggregated by investment category for available-for-sale investments as of September 30, 2018 and December 31, 2017, reflect the inclusion within short-term investments of investments with contractual maturities greater than one year from the date of purchase. Management has the ability, if necessary, to liquidate any of its investments in order to meet the Company’s liquidity needs in the next 12 months. Accordingly, those investments with contractual maturities greater than one year from the date of purchase are classified as short-term on the accompanying balance sheets.

The Company reviews and evaluates its investments for any indication of possible impairment. Based on this review, the Company has determined that the unrealized losses related to these investments at September 30, 2018 and December 31, 2017 were temporary.

Interest income is accrued as earned. Dividend income is recognized as income on the date the stock trades “ex-dividend.” The cost of marketable securities sold is determined by the specific identification method. Realized gains or losses are reflected in income and were not material for the nine months ended September 30, 2018 and 2017.