Fair Value Measurement: (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Thousands, unless otherwise specified	Sep. 30, 2014 Carrying (Reported) Amount, Fair Value Disclosure [Member]	Dec. 31, 2013 Carrying (Reported) Amount, Fair Value Disclosure [Member]	Sep. 30, 2014 Quoted prices in active markets for identical assets (level 1) Certificates of Deposit [Member]	Dec. 31, 2013 Quoted prices in active markets for identical assets (level 1) Certificates of Deposit [Member]	Sep. 30, 2014 Signifcant other observable inputs (level 2) Available-for-sale Securities [Member]	Dec. 31, 2013 Signifcant other observable inputs (level 2) Available-for-sale Securities [Member]	Jun. 30, 2014 Significant unobservable inputs (level 3)	Dec. 31, 2013 Significant unobservable inputs (level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities	$ 77,503	$ 70,869	$ 5,665	$ 3,205	$ 71,838	$ 67,664	$ 0	$ 0