Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current tax expense:
Federal	$ 33,456	$ 25,229	$ 19,956
State	5,696	6,131	4,311
Total	39,152	31,360	24,267
Deferred tax expense/(benefit):
Federal	(6,085)	1,971	2,191
State	(238)	(153)	125
Total	(6,323)	1,818	2,316
Total income tax expense	32,829	33,178	26,583
Income tax expense
Computed at federal statutory rate	29,171	28,337	23,336
State and local tax expense, net of federal benefit	3,548	3,907	2,894
Other, net	110	934	353
Total income tax expense	$ 32,829	$ 33,178	$ 26,583
Income tax rate (as a percent)
Computed at federal statutory rate (as a percent)	35.00%	35.00%	35.00%
State and local tax expense, net of federal benefit (as a percent)	4.30%	4.80%	4.30%
Other, net (as a percent)	0.10%	1.20%	0.60%
Total income tax expense (as a percent)	39.40%	41.00%	39.90%
Effective income tax rate (as a percent)	39.40%	41.00%	39.90%