Investments and Fair Value Measurements - Investment Category and Length (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2017 USD ($) entity	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) entity	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]
Fair value, in loss position less than twelve months	$ 26,015,000		$ 26,015,000		$ 10,248,000
Gross unrealized loss, in loss position less than twelve months			(77,000)		(55,000)
Fair value, in loss position greater than twelve months	3,567,000		3,567,000		4,595,000
Gross unrealized loss, in loss position greater than twelve months			(4,000)		(12,000)
Fair value, total in loss position	29,582,000		29,582,000		14,843,000
Gross unrealized loss, total in loss position			(81,000)		(67,000)
Minority Investments
Investments in privately-held companies	$ 6,192,000		$ 6,192,000		6,599,000
Number of gallium companies with impairment charge | entity	1		1
Equity method investments | entity			7
Impairment charge	$ 0	$ 0		$ 0
Investments held	6,192,000		$ 6,192,000		6,599,000
One Gallium Company
Minority Investments
Investments in privately-held companies	0		0			$ 0
Impairment charge	0		313,000
Investments held	0		0			$ 0
Certificates of Deposit [Member]
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]
Fair value, in loss position less than twelve months	2,391,000		2,391,000		5,211,000
Gross unrealized loss, in loss position less than twelve months			(9,000)		(20,000)
Fair value, in loss position greater than twelve months	1,867,000		1,867,000		1,200,000
Gross unrealized loss, in loss position greater than twelve months			(3,000)
Fair value, total in loss position	4,258,000		4,258,000		6,411,000
Gross unrealized loss, total in loss position			(12,000)		(20,000)
Corporate Bonds [Member]
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]
Fair value, in loss position less than twelve months	23,624,000		23,624,000		5,037,000
Gross unrealized loss, in loss position less than twelve months			(68,000)		(35,000)
Fair value, in loss position greater than twelve months	1,700,000		1,700,000		3,395,000
Gross unrealized loss, in loss position greater than twelve months			(1,000)		(12,000)
Fair value, total in loss position	25,324,000		25,324,000		8,432,000
Gross unrealized loss, total in loss position			(69,000)		(47,000)
Other Assets [Member]
Minority Investments
Investments in privately-held companies	10,300,000		10,300,000		11,300,000
Investments held	$ 10,300,000		$ 10,300,000		$ 11,300,000