General - Investments (Details) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Short-term and long-term investments
Other-than-temporary unrealized losses	$ 0		$ 0
Realized gains or losses	0	$ 0
Amortized Cost	287,699		326,589
Gross Unrealized Gains	52		4
Gross Unrealized Losses	(93)		(428)
Estimated Fair Value	287,658		326,165
U.S. Government and agency securities
Short-term and long-term investments
Amortized Cost	5,126		5,524
Gross Unrealized Gains	6
Gross Unrealized Losses			(10)
Estimated Fair Value	5,132		5,514
Obligations of government-sponsored enterprises
Short-term and long-term investments
Amortized Cost	54,688		50,575
Gross Unrealized Gains	20		4
Gross Unrealized Losses			(54)
Estimated Fair Value	54,708		50,525
Corporate debt securities
Short-term and long-term investments
Amortized Cost	226,735		269,340
Gross Unrealized Gains	26
Gross Unrealized Losses	(93)		(364)
Estimated Fair Value	226,668		268,976
Certificates of deposit
Short-term and long-term investments
Amortized Cost	1,150		1,150
Estimated Fair Value	$ 1,150		$ 1,150