Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Deferred tax liabilities [Abstract]
Prepaid assets	$ (6,929,000)	$ (9,268,000)
Depreciation	(8,580,000)	(8,616,000)
Software development costs	(3,104,000)	(2,858,000)
Amortization	0	(1,210,000)
Total deferred tax liabilities	(18,613,000)	(21,952,000)
Deferred tax assets [Abstract]
Accrued incentive compensation	4,896,000	3,877,000
Net operating loss carryforward	2,057,000	2,290,000
Workers' compensation accruals	5,079,000	3,744,000
Accrued rent	1,033,000	1,132,000
Stock-based compensation	3,114,000	2,908,000
Uncollectible accounts receivable	645,000	610,000
Total deferred tax assets	16,824,000	14,561,000
Valuation allowance	0	(148,000)
Total net deferred tax assets	16,824,000	14,413,000
Net deferred tax liabilities	(1,789,000)	(7,539,000)
Net current deferred tax assets (liabilities)	7,211,000	3,233,000
Net noncurrent deferred tax liabilities	(9,000,000)	(10,772,000)
Current income tax expense [Abstract]
Federal	29,280,000	16,816,000	12,668,000
State	4,351,000	3,535,000	1,734,000
Total current income tax expense	33,631,000	20,351,000	14,402,000
Deferred income tax (benefit) expense [Abstract]
Federal	(5,363,000)	47,000	1,033,000
State	(380,000)	(93,000)	146,000
Total deferred income tax (benefit) expense	(5,743,000)	(46,000)	1,179,000
Total income tax expense	27,888,000	20,305,000	15,581,000
Net income tax expense (benefit) on nonqualified stock option exercises	1,751,000	1,663,000	25,000
Reconciliation of income tax expense [Abstract]
Assumed income tax rate (in hundredths)	35.00%
Expected income tax expense at 35%	23,901,000	17,770,000	13,307,000
State income taxes, net of federal benefit	2,497,000	2,249,000	1,273,000
Nondeductible expenses	1,663,000	904,000	1,092,000
Research and development credit	0	(558,000)	0
Other, net	(173,000)	(60,000)	(91,000)
Reported total income tax expense	27,888,000	20,305,000	15,581,000
Capital loss carryforwards	55,000
Capital loss carryforwards, expiration date	December 31, 2012
Valuation allowance for capital loss carryforward	345,000
Business Acquisition [Line Items]
Net operating loss carryforwards	2,057,000	2,290,000
ExpensAble [Member]
Deferred tax assets [Abstract]
Net operating loss carryforward	5,400,000
Business Acquisition [Line Items]
Net operating loss carryforwards	$ 5,400,000
Net operating loss carryforwards, expiration date	2021 to 2030