Stock Option Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Option Plans [Abstract]
Number of stock compensation plans	2
Compensation Expense [Abstract]
Total stock-based compensation expense	$ 7,666,000	$ 5,310,000	$ 4,627,000
Tax benefit	(2,836,000)	(1,964,000)	(1,712,000)
Stock-based compensation expense, net of tax	4,830,000	3,346,000	2,915,000
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, minimum (in years)	P2Y
Vesting period, maximum (in years)	P4Y
Compensation Expense [Abstract]
Total stock-based compensation expense	5,162,000	4,881,000	4,627,000
Valuation Assumptions [Abstract]
Expected dividend yield, minimum (in hundredths)	0.64%	0.60%	0.94%
Expected dividend yield, maximum (in hundredths)	1.02%	0.80%	1.60%
Expected stock price volatility, minimum (in hundredths)	45.00%	48.10%	51.20%
Expected stock price volatility, maximum (in hundredths)	56.40%	57.90%	57.80%
Risk free interest rate, minimum (in hundredths)	0.27%	0.28%	0.53%
Risk free interest rate, maximum (in hundredths)	0.82%	2.39%	2.96%
Expected life options, minimum (in years)	2	3	2
Expected life options, maximum (in years)	4	4	6
Weighted-average fair value per share at grant date (in dollars per share)	$ 63.84	$ 26.29	$ 17.05
Stock Options, Shares [Roll Forward]
Outstanding, beginning of period (in shares)	1,504,311
Granted (in shares)	236,800
Exercised (in shares)	(71,026)
Forfeited or expired (in shares)	(44,758)
Outstanding, end of period (in shares)	1,625,327	1,504,311
Exercisable, end of period (in shares)	921,461
Weighted-Average Exercise Price [Abstract]
Outstanding, beginning of period (in dollars per share)	$ 42.26
Granted (in dollars per share)	$ 50.58
Exercised (in dollars per share)	$ 27.46
Forfeited or expired (in dollars per share)	$ 48.04
Outstanding, end of period (in dollars per share)	$ 43.96	$ 42.26
Exercisable, end of period (in dollars per share)	$ 38.37
Weighted-Average Remaining Contractual Term [Abstract]
Outstanding, end of period (in years)	7.3
Exercisable, end of period (in years)	6.4
Aggregate Intrinsic Value [Abstract]
Outstanding, end of period	25,474,000
Exercisable, end of period	19,430,000
Unrecognized compensation expense	4,800,000
Weighted-average period of cost recognition (in years)	1.96
Intrinsic value of stock options exercised	3,400,000	9,200,000	11,400,000
Stock Options [Member] | Granted to Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration term (in years)	P10Y
Stock Options [Member] | Granted to Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration term (in years)	P10Y
Restricted Stock Awards and Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, maximum (in years)	P3Y
Compensation Expense [Abstract]
Total stock-based compensation expense	2,216,000	429,000	0
Aggregate Intrinsic Value [Abstract]
Unrecognized compensation expense	7,700,000	2,900,000
Weighted-average period of cost recognition (in years)	2.3
Number of Awards [Abstract]
Outstanding, beginning of period (in shares)	57,300
Granted (in shares)	74,705	57,300
Vested (in shares)	(19,102)
Forfeited (in shares)	(2,996)
Outstanding, end of period (in shares)	109,907	57,300
Weighted-Average Grant Date Fair Value [Roll Forward]
Outstanding, beginning of period (in dollars per share)	$ 57.40
Granted (in dollars per share)	$ 62.36
Vested (in dollars per share)	$ 57.40
Forfeited (in dollars per share)	$ 79.64
Outstanding, end of period (in dollars per share)	$ 60.13	$ 57.40
Performance Shares [Member]
Compensation Expense [Abstract]
Total stock-based compensation expense	288,000	0	0
Aggregate Intrinsic Value [Abstract]
Unrecognized compensation expense	$ 3,900,000
Weighted-average period of cost recognition (in years)	1.5
Number of Awards [Abstract]
Outstanding, beginning of period (in shares)	0
Granted (in shares)	70,151
Forfeited (in shares)	(2,996)
Outstanding, end of period (in shares)	67,155	0
Weighted-Average Grant Date Fair Value [Roll Forward]
Outstanding, end of period (in dollars per share)	$ 59.55