Investment in Securities (Schedule of the Fair Values of Securities with Unrealized Losses) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Investment [Line Items]
Estimated fair value less than 12 months	$ 8,700	$ 101,792
Estimated fair value 12 months or more	13,833	3,554
Estimated fair value total	22,533	105,346
Unrealized losses, 12 months or more	183	262
Unrealized losses, less than 12 months	15	2,661
Unrealized losses, total	198	2,923
State and Political Subdivisions [Member]
Investment [Line Items]
Estimated fair value less than 12 months	8,700	101,792
Estimated fair value 12 months or more	13,833	3,554
Estimated fair value total	22,533	105,346
Unrealized losses, 12 months or more	183	262
Unrealized losses, less than 12 months	15	2,661
Unrealized losses, total	198	2,923
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