Investment Securities: (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Debt Securities Maturity Date Range Low	2014
Debt Securities Maturity Date Range High	2040
Investment securities	$ 76,224	$ 70,869	[1]
Federal tax-exempt debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment securities	22,375	21,968
Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment securities	48,309	45,696
Certificates of deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment securities	$ 5,540	$ 3,205

[1] December 31, 2013 balances were derived from audited consolidated financial statements.