INVESTMENTS: (Fair value due by period) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Amortized Cost
Due in less than one year	$ 155,609	$ 157,270
Due in one to three years	111,391	114,627
Available-for-sale securities, amortized cost basis	267,000	271,897
Estimated Fair Value
Due in less than one year	155,499	157,163
Due in one to three years	111,334	114,498
Estimated fair value	266,833	271,661
Investment in a privately-held companies accounted for under the cost method	$ 19,700	$ 12,700