Marketable Securities - Summary of Marketable Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	$ 115,218,000	$ 79,885,000
Unrealized Gains	1,234,000	1,561,000
Unrealized Losses	(1,472,000)	(1,708,000)
Fair Value	114,980,000	79,738,000
Gross realized gain	1,265,000	241	$ 24
Gross realized loss	586,000	677	$ 81
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	3,689,000	3,510,000
Unrealized Gains	409,000	29,000
Unrealized Losses	(65,000)	(14,000)
Fair Value	4,033,000	3,525,000
Time deposits
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost		13,641,000
Unrealized Gains		0
Unrealized Losses		0
Fair Value		13,641,000
Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	57,871,000	42,129,000
Unrealized Gains	89,000	1,520,000
Unrealized Losses	(612,000)	(1,510,000)
Fair Value	57,348,000	42,139,000
Government securities - U.S.
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	43,049,000	13,822,000
Unrealized Gains	515,000	4,000
Unrealized Losses	(750,000)	(88,000)
Fair Value	42,814,000	13,738,000
Government securities - Non-U.S.
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	247,000	1,112,000
Unrealized Gains	0	8,000
Unrealized Losses	(14,000)	(57,000)
Fair Value	233,000	1,063,000
Other fixed-income securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	10,281,000	4,008,000
Unrealized Gains	221,000	0
Unrealized Losses	(31,000)	(16,000)
Fair Value	10,471,000	3,992,000
Other securities
Schedule of Available-for-sale Securities [Line Items]
Adjusted Cost	81,000	1,663,000
Unrealized Gains	0	0
Unrealized Losses	0	(23,000)
Fair Value	$ 81,000	$ 1,640,000