Federal Income Taxes (Provision for Federal Income Taxes) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosure [Abstract]
Current income tax expense									$ 8,132	$ 10,787	$ 4,661
Deferred income tax expense									12,668	6,413	3,439
Total provision for federal income taxes	$ 4,000	$ 5,300	$ 6,325	$ 5,175	$ 4,475	$ 4,075	$ 4,750	$ 3,900	$ 20,800	$ 17,200	$ 8,100