Investments (Tables)

12 Months Ended

Dec. 31, 2017

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