Short-Term and Long-Term Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total available for sale short-term and long-term marketable securities	$ 383,133	$ 310,764
Fair Value, Measurements, Recurring [Member] | Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	284,681	251,086
Gross Unrealized Gains	30	38
Gross Unrealized Losses	(152)	(143)
Total available for sale short-term and long-term marketable securities	284,559	250,981
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,160	42,397
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(6)
Total available for sale short-term and long-term marketable securities	42,160	42,391
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	152,169	122,788
Gross Unrealized Gains	30	22
Gross Unrealized Losses	(107)	(121)
Total available for sale short-term and long-term marketable securities	152,092	122,689
Fair Value, Measurements, Recurring [Member] | Short-term Investments | U.S. government agency bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,879	28,903
Gross Unrealized Gains	0	9
Gross Unrealized Losses	(16)	(4)
Total available for sale short-term and long-term marketable securities	21,863	28,908
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Municipal securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,853	5,852
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(5)
Total available for sale short-term and long-term marketable securities	3,852	5,847
Fair Value, Measurements, Recurring [Member] | Short-term Investments | U.S. government treasury bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	54,767	45,146
Gross Unrealized Gains	0	7
Gross Unrealized Losses	(28)	(7)
Total available for sale short-term and long-term marketable securities	54,739	45,146
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,787	6,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Total available for sale short-term and long-term marketable securities	9,787	6,000
Fair Value, Measurements, Recurring [Member] | Short-term Investments | Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	66
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Total available for sale short-term and long-term marketable securities	66
Fair Value, Measurements, Recurring [Member] | Long-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	98,596	59,887
Gross Unrealized Gains	70	13
Gross Unrealized Losses	(92)	(117)
Total available for sale short-term and long-term marketable securities	98,574	59,783
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	79,267	40,889
Gross Unrealized Gains	48	8
Gross Unrealized Losses	(65)	(85)
Total available for sale short-term and long-term marketable securities	79,250	40,812
Fair Value, Measurements, Recurring [Member] | Long-term Investments | U.S. government agency bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,295	6,805
Gross Unrealized Gains	19	0
Gross Unrealized Losses	(12)	(16)
Total available for sale short-term and long-term marketable securities	11,302	6,789
Fair Value, Measurements, Recurring [Member] | Long-term Investments | U.S. government treasury bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,034	12,016
Gross Unrealized Gains	3	5
Gross Unrealized Losses	(15)	(16)
Total available for sale short-term and long-term marketable securities	$ 8,022	12,005
Fair Value, Measurements, Recurring [Member] | Long-term Investments | Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		177
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Total available for sale short-term and long-term marketable securities		$ 177