Share-Based Compensation (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				0 Months Ended		3 Months Ended
	Mar. 31, 2013 Stock Options	Mar. 31, 2013 Incentive stock options	Mar. 31, 2013 2012 plan	Mar. 31, 2013 2012 plan Restricted Stock Maximum	Jan. 02, 2004 1999 plan	Jan. 26, 2012 2004 plan	Mar. 31, 2013 1999, 2004 and 2012 Plans Incentive stock options
Share-Based Compensation
Vesting percentage							25.00%
Vesting period		4 years
Expiration period		10 years
Number of shares registered under the 2012 plan			1,684,000	817,476
Number of shares
Outstanding at the beginning of the period (in shares)	340,140
Granted (in shares)	23,007				0	0
Exercised (in shares)	(18,211)
Expired/Forfeited (in shares)	(1,444)
Outstanding at the end of the period (in shares)	343,492
Exercisable at the end of the period (in shares)	280,629
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 31.79
Granted (in dollars per share)	$ 41.45
Exercised (in dollars per share)	$ 28.34
Expired/Forfeited (in dollars per share)	$ 22.13
Outstanding at the end of the period (in dollars per share)	$ 32.66
Exercisable at the end of the period (in dollars per share)	$ 32.04
Weighted-average fair value of options granted during the year (in dollars per share)	$ 15.66
Weighted-Average Remaining Contractual Life
Outstanding at the end of the period	4 years 11 months 26 days
Exercisable at the end of the period	4 years 2 months 5 days
Aggregate Intrinsic Value (000's)
Outstanding at the end of the period	$ 6,095
Exercisable at the end of the period	$ 5,153