Investment in Securities (Schedule of Investement Securities) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Amortized Cost	$ 268,606	$ 322,087
Gross Unrealized Gains	10,650	19,960
Gross Unrealized Losses	2,828	112
Fair Value	276,428	341,935
State and Political Subdivisions [Member]
Amortized Cost	262,797	315,345
Gross Unrealized Gains	10,650	19,960
Gross Unrealized Losses	2,828	112
Fair Value	270,619	335,193
Certificates Of Deposit [Member]
Amortized Cost	5,809	6,742
Gross Unrealized Gains
Gross Unrealized Losses
Fair Value	$ 5,809	$ 6,742