Noncontrolling Interests (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Redeemable Noncontrolling Interest [Line Items]
Noncontrolling interest, Income Statement Impact	$ 806,000	$ 840,000	$ 757,000
Redemption value change, Income Statement Impact	156,000	716,000	0
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	962,000	1,555,000	757,000
Net income attributable to noncontrolling interests	5,165,000	4,455,000	3,915,000
Formation of noncontrolling interests, Redeemable Noncontrolling Interests		510,000	1,390,000
Distribution to noncontrolling interests, Redeemable Noncontrolling Interests	935,000	901,000	717,000
Beginning balance, Redeemable Noncontrolling Interests	6,964,000	5,799,000	4,369,000
Ending balance, Redeemable Noncontrolling Interests	6,991,000	6,964,000	5,799,000
Tax Benefit from Stock Options Exercised	3,900,000	2,200,000	1,300,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	3,100,000	2,200,000	2,100,000
Noncontrolling Interest [Member]
Redeemable Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest		$ 1,556,000