FAIR VALUE MEASUREMENTS (Details ) - Recurring basis - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair value
Assets, Total	$ 575,840	$ 673,146
Level 1
Fair value
Assets, Total	163,728	216,122
Level 2
Fair value
Assets, Total	353,961	399,903
Level 3
Fair value
Assets, Total	58,151	57,121
Cash equivalents
Fair value
Estimated Fair Value	1,667	1,666
Cash equivalents | Level 1
Fair value
Estimated Fair Value	1,667	1,666
U.S. government and agency debt securities
Fair value
Estimated Fair Value	290,336	352,188
U.S. government and agency debt securities | Level 1
Fair value
Estimated Fair Value	162,061	214,456
U.S. government and agency debt securities | Level 2
Fair value
Estimated Fair Value	128,275	137,732
Corporate debt securities
Fair value
Estimated Fair Value	190,696	213,209
Corporate debt securities | Level 2
Fair value
Estimated Fair Value	190,696	213,209
International government agency debt securities
Fair value
Estimated Fair Value	34,990	48,962
International government agency debt securities | Level 2
Fair value
Estimated Fair Value	34,990	48,962
Contingent Consideration
Fair value
Assets, Total	57,200	55,300
Contingent Consideration | Level 3
Fair value
Assets, Total	57,200	55,300
Equity securities
Fair value
Estimated Fair Value	951	1,821
Equity securities | Level 3
Fair value
Estimated Fair Value	$ 951	$ 1,821