ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS): (AOCI rollforward) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	$ 975,730
Realized (gains)/losses reclassified from accumulated other comprehensive income	1,440	$ (422)
Other comprehensive income, net of tax	4,313	4,092
Ending Balance	994,243
Unrealized gains (losses) on available-for-sale securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(236)	(578)
Other comprehensive income/(loss) before reclassifications, net of taxes	73	40
Realized (gains)/losses reclassified from accumulated other comprehensive income	(4)	560
Other comprehensive income, net of tax	69	600
Ending Balance	(167)	22
Unrealized gains (losses) on derivatives designated as hedging instruments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(692)	(1,091)
Other comprehensive income/(loss) before reclassifications, net of taxes	5,680	3,630
Realized (gains)/losses reclassified from accumulated other comprehensive income	(1,436)	(138)
Other comprehensive income, net of tax	4,244	3,492
Ending Balance	3,552	2,401
Total [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning Balance	(928)	(1,669)
Other comprehensive income/(loss) before reclassifications, net of taxes	5,753	3,670
Realized (gains)/losses reclassified from accumulated other comprehensive income	(1,440)	422
Other comprehensive income, net of tax	4,313	4,092
Ending Balance	$ 3,385	$ 2,423