INVESTMENTS (Fair value due by period) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Amortized Cost
Due in less than one year	$ 204,399	$ 157,270
Due in one to three years	83,569	114,627
Available-for-sale securities, amortized cost basis	287,968	271,897
Estimated Fair Value
Due in less than one year	204,315	157,163
Due in one to three years	83,428	114,498
Estimated Fair Value	287,743	271,661
Investment in a privately-held companies accounted for under the cost method	$ 22,200	$ 12,700