Short-Term and Long-Term Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Total available for sale short-term and long-term marketable securities	$ 255,838	$ 510,951
Fair Value, Measurements, Recurring [Member] | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	192,978	359,956
Gross Unrealized Gains	73	14
Gross Unrealized Losses	(33)	(389)
Total available for sale short-term and long-term marketable securities	193,018	359,581
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,029	38,537
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Total available for sale short-term and long-term marketable securities	19,029	38,537
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	81,955	179,765
Gross Unrealized Gains	18	6
Gross Unrealized Losses	(29)	(251)
Total available for sale short-term and long-term marketable securities	81,944	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	30,587	75,172
Gross Unrealized Gains	24	0
Gross Unrealized Losses	0	(53)
Total available for sale short-term and long-term marketable securities	30,611	75,119
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,205	14,209
Gross Unrealized Gains	0	7
Gross Unrealized Losses	(4)	(2)
Total available for sale short-term and long-term marketable securities	9,201	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		510
Gross Unrealized Gains		0
Gross Unrealized Losses		(2)
Total available for sale short-term and long-term marketable securities		508
Fair Value, Measurements, Recurring [Member] | Short-term Investments | U.S. government treasury bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	47,702	51,763
Gross Unrealized Gains	31	1
Gross Unrealized Losses	0	(81)
Total available for sale short-term and long-term marketable securities	47,733	51,683
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,500
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Total available for sale short-term and long-term marketable securities	4,500
Fair Value, Measurements, Recurring [Member] | Long-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	62,677	151,869
Gross Unrealized Gains	150	9
Gross Unrealized Losses	(7)	(508)
Total available for sale short-term and long-term marketable securities	62,820	151,370
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43,101	64,012
Gross Unrealized Gains	118	9
Gross Unrealized Losses	(7)	(218)
Total available for sale short-term and long-term marketable securities	43,212	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	9,249	43,853
Gross Unrealized Gains	11	0
Gross Unrealized Losses	0	(178)
Total available for sale short-term and long-term marketable securities	9,260	43,675
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	300	2,338
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(3)
Total available for sale short-term and long-term marketable securities	300	2,335
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		3,993
Gross Unrealized Gains		0
Gross Unrealized Losses		(2)
Total available for sale short-term and long-term marketable securities		3,991
Fair Value, Measurements, Recurring [Member] | Long-term Investments | U.S. government treasury bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,027	37,673
Gross Unrealized Gains	21	0
Gross Unrealized Losses	0	(107)
Total available for sale short-term and long-term marketable securities	$ 10,048	$ 37,566