Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Currently payable:
Federal	$ 131,000	$ 104,922	$ 93,677
State	12,197	9,335	9,033
Foreign	37
Total currently payable	143,234	114,257	102,710
Deferred taxes	(3,001)	(5,782)	2,004
Provision for income taxes	$ 140,233	$ 108,475	$ 104,714
Reconciliation of statutory federal income tax rate with the entity's effective income tax rate
Statutory federal income tax rate (as a percent)	35.00%	35.00%	35.00%
State income taxes, net of federal tax benefits (as a percent)	2.20%	2.20%	2.40%
State tax incentives (as a percent)	(0.10%)	(0.20%)	(0.20%)
Valuation allowance on losses capital in nature (as a percent)	(1.80%)	(0.80%)	(0.20%)
Other items (as a percent)	0.40%	(0.20%)	0.80%
Effective income tax rate (as a percent)	35.70%	36.00%	37.80%