General - Investments (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Short-term and long-term investments
Realized gains or losses	$ 0	$ 0
Amortized Cost	430,377		$ 386,169
Gross Unrealized Gains	126		23
Gross Unrealized Losses	(132)		(449)
Estimated Fair Value	430,371		385,743
U.S. Government and agency securities
Short-term and long-term investments
Amortized Cost	109,476		67,870
Gross Unrealized Gains	62		17
Gross Unrealized Losses	(34)		(72)
Estimated Fair Value	109,504		67,815
Obligations of government-sponsored enterprises
Short-term and long-term investments
Amortized Cost	5,255		5,257
Gross Unrealized Losses	(11)		(28)
Estimated Fair Value	5,244		5,229
Corporate debt securities
Short-term and long-term investments
Amortized Cost	295,496		292,392
Gross Unrealized Gains	64		6
Gross Unrealized Losses	(87)		(349)
Estimated Fair Value	295,473		292,049
Certificates of deposit
Short-term and long-term investments
Amortized Cost	20,150		20,650
Estimated Fair Value	$ 20,150		$ 20,650

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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-Publisher FASB
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