Investment in Securities (Schedule of the Fair Values of Securities with Unrealized Losses) (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Investment [Line Items]
Estimated fair value, less than 12 months	$ 103,552	$ 8,700
Estimated fair value, 12 months or more	1,195	13,833
Estimated fair value, total	104,747	22,533
Unrealized losses, 12 months or more	1,164	15
Unrealized losses, less than 12 months	38	183
Unrealized losses, total	1,202	198
State and Political Subdivisions [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	103,552	8,700
Estimated fair value, 12 months or more	1,195	13,833
Estimated fair value, total	104,747	22,533
Unrealized losses, 12 months or more	1,164	15
Unrealized losses, less than 12 months	38	183
Unrealized losses, total	$ 1,202	$ 198
Certificates Of deposit [Member]
Investment [Line Items]
Estimated fair value, less than 12 months
Estimated fair value, 12 months or more
Estimated fair value, total
Unrealized losses, 12 months or more
Unrealized losses, less than 12 months
Unrealized losses, total