Significant Accounting Policies (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Significant Accounting Policies [Line Items]
DeferredTaxAssetsReclassification	$ 29,400,000
Noncash or Part Noncash Acquisition, Fixed Assets Acquired	3,552,000	$ 0	$ 0
Stock Repurchase Program, Authorized Amount	200,000,000
Debt and Capital Lease Obligations	133,805,000	155,714,000
Depreciation expenses including capital leases	164,800,000	145,800,000	126,400,000
Self-insurance reserve	119,200,000	107,700,000
Long-term portions of self insurance reserve	74,300,000	65,400,000
Advertising expense	22,900,000	19,300,000	$ 16,700,000
Long-term Debt, Fair Value	$ 139,100,000	$ 165,500,000
Total Stock Repurchased And Retired Shares	1,753,039
Total Stock Repurchased And Retired Value	$ 119,600,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	80,400,000
Group Health Claims [Member]
Significant Accounting Policies [Line Items]
Insurance maximum, per occurrence	500,000
Self insurance additional coverage	400,000
Workers Compensation Claims [Member]
Significant Accounting Policies [Line Items]
Insurance maximum, per occurrence	1,000,000
Cargo Loss And Damage Claims [Member]
Significant Accounting Policies [Line Items]
Insurance maximum, per occurrence	100,000
Bodily Injury And Property Damage [Member]
Significant Accounting Policies [Line Items]
Insurance maximum, per occurrence	$ 2,750,000