4)	Investments

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


	June 30, 2018		December 31, 2017
Available-for-sale investments:
Time deposits and certificates of deposit	$	18,455	$	9,757
Bankers’ acceptance drafts		2,522		5,330
Asset-backed securities		34,727		36,990
Commercial paper		25,925		13,750
Corporate obligations		66,663		77,821
Municipal bonds		2,615		1,970
U.S. treasury obligations		31,434		28,078
U.S. agency obligations		21,345		35,738

	$	203,686	$	209,434

Investments classified as long-term consist of the following:


	June 30, 2018		December 31, 2017
Available-for-sale investments:
Group insurance contracts	$	6,076	$	6,255
Cost method investments:
Minority interest in a private company		4,400		4,400

	$	10,476	$	10,655

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


As of June 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	$	18,452	$	3	$	—		$	18,455
Bankers’ acceptance drafts		2,522		—		—			2,522
Asset-backed securities		34,760		9		(42	)		34,727
Commercial paper		26,337		—		(412	)		25,925
Corporate obligations		66,632		59		(28	)		66,663
Municipal bonds		2,620		—		(5	)		2,615
U.S. treasury obligations		31,418		16		—			31,434
U.S. agency obligations		21,341		5		(1	)		21,345

	$	204,082	$	92	$	(488	)	$	203,686


As of June 30, 2018:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
Long-term investments:
Available-for-sale investments:
Group insurance contracts	$	6,051	$	25	$	—		$	6,076


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 June 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 June 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 six months ended June 30, 2018 and 2017.