5)	Investments

Investments classified as short-term consist of the following:


	Years Ended December 31,
Available-for-sale investments:	2017		2016
Time deposits and certificates of deposit	$	9,757	$	23,818
Bankers’ acceptance drafts		5,330		1,439
Asset-backed securities		36,990		36,809
Commercial paper		13,750		24,381
Corporate obligations		77,821		46,707
Municipal bonds		1,970		591
Promissory note		—		675
U.S. treasury obligations		28,078		25,414
U.S. agency obligations		35,738		29,629

	$	209,434	$	189,463

Investments classified as long-term consist of the following:


	Years Ended December 31,
Available-for-sale investments:	2017		2016
Group insurance contracts	$	6,255	$	5,558
Cost method investments:
Minority interest in a private company(1)		4,400		4,300

	$	10,655	$	9,858

(1)	In April of 2016 the Company invested $9,300 for a minority interest in a private company. During 2016, the Company recognized $5,000 of impairment charges related to this cost method investment. In July 2017, the Company invested an additional $100 in this private company.

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


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


As of December 31, 2016:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)			Estimated Fair Value
Short-term investments:
Available-for-sale investments:
Time deposits and certificates of deposit	$	23,818	$	—	$	—		$	23,818
Bankers acceptance drafts		1,439		—		—			1,439
Asset-backed securities		36,847		6		(44	)		36,809
Commercial paper		24,423		—		(42	)		24,381
Corporate obligations		46,700		21		(14	)		46,707
Municipal bonds		591		—		—			591
Promissory note		675		—		—			675
U.S. treasury obligations		25,414		—		—			25,414
U.S. agency obligations		29,631		8		(10	)		29,629

	$	189,538	$	35	$	(110	)	$	189,463


As of December 31, 2016:	Cost		Gross Unrealized Gains		Gross Unrealized (Losses)		Estimated Fair Value
Long-term investments:
Available-for-sale investments:
Group insurance contracts	$	5,432	$	126	$	—	$	5,558

The tables above, which show the gross unrealized gains and (losses) aggregated by investment category for available-for-sale investments as of December 31, 2017 and 2016, 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.

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 and realized gains or losses are reflected in income and were not material in 2017, 2016 and 2015.