Investments (Investments in Marketable Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Available-for-sale — short-term:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 40,551	$ 23,271
Gross Unrealized Gains	1	0
Gross Unrealized Losses	(2)	(22)
Fair Value	40,550	23,249
Available-for-sale — short-term: | U.S. Treasury, government and agency debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,237	10,485
Gross Unrealized Gains	1	0
Gross Unrealized Losses	(2)	(22)
Fair Value	23,236	10,463
Available-for-sale — short-term: | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,314	12,786
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 17,314	12,786
Available-for-sale — long-term: | U.S. Treasury, government and agency debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		13,529
Gross Unrealized Gains		0
Gross Unrealized Losses		(46)
Fair Value		$ 13,483