Short-Term and Long-Term Marketable Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Total available for sale short-term and long-term marketable securities	$ 517,265	$ 510,951
Fair Value, Measurements, Recurring [Member] | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	403,874	359,956
Gross Unrealized Gains	257	14
Gross Unrealized Losses	(24)	(389)
Total available for sale short-term and long-term marketable securities	404,107	359,581
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	61,412	38,537
Gross Unrealized Gains	19	0
Gross Unrealized Losses	0	0
Total available for sale short-term and long-term marketable securities	61,431	38,537
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	178,415	179,765
Gross Unrealized Gains	109	6
Gross Unrealized Losses	(20)	(251)
Total available for sale short-term and long-term marketable securities	178,504	179,520
Fair Value, Measurements, Recurring [Member] | Short-term Investments | U.S. government agency bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	76,743	75,172
Gross Unrealized Gains	39	0
Gross Unrealized Losses	(4)	(53)
Total available for sale short-term and long-term marketable securities	76,778	75,119
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,365	14,209
Gross Unrealized Gains	9	7
Gross Unrealized Losses	0	(2)
Total available for sale short-term and long-term marketable securities	10,374	14,214
Fair Value, Measurements, Recurring [Member] | Short-term Investments | U.S. dollar dominated foreign corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	503	510
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(2)
Total available for sale short-term and long-term marketable securities	503	508
Fair Value, Measurements, Recurring [Member] | Short-term Investments | U.S. government treasury bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	73,936	51,763
Gross Unrealized Gains	81	1
Gross Unrealized Losses	0	(81)
Total available for sale short-term and long-term marketable securities	74,017	51,683
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Total available for sale short-term and long-term marketable securities	2,500
Fair Value, Measurements, Recurring [Member] | Long-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	112,783	151,869
Gross Unrealized Gains	382	9
Gross Unrealized Losses	(7)	(508)
Total available for sale short-term and long-term marketable securities	113,158	151,370
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	78,919	64,012
Gross Unrealized Gains	294	9
Gross Unrealized Losses	(7)	(218)
Total available for sale short-term and long-term marketable securities	79,206	63,803
Fair Value, Measurements, Recurring [Member] | Long-term Investments | U.S. government agency bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,254	43,853
Gross Unrealized Gains	26	0
Gross Unrealized Losses	0	(178)
Total available for sale short-term and long-term marketable securities	13,280	43,675
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	494	2,338
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(3)
Total available for sale short-term and long-term marketable securities	494	2,335
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,342	3,993
Gross Unrealized Gains	4	0
Gross Unrealized Losses	0	(2)
Total available for sale short-term and long-term marketable securities	3,346	3,991
Fair Value, Measurements, Recurring [Member] | Long-term Investments | U.S. dollar dominated foreign corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Total available for sale short-term and long-term marketable securities	2,712
Fair Value, Measurements, Recurring [Member] | Long-term Investments | U.S. government treasury bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	14,062	37,673
Gross Unrealized Gains	58	0
Gross Unrealized Losses	0	(107)
Total available for sale short-term and long-term marketable securities	14,120	$ 37,566
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,712
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Total available for sale short-term and long-term marketable securities	$ 2,712