Stock Options and Other Equity-Based Incentive Instruments (Details) (USD $)	3 Months Ended
	Mar. 31, 2013
Stock option activity
Outstanding at December 31, 2012, Number of shares	1,393,935
Outstanding at December 31, 2012, Weighted Average Exercise Price	$ 17.07
Options granted, Number of Shares	7,500
Options granted, Weighted Average Exercise Price	$ 16.59
Options granted, Weighted Average Fair Value on Date of Grant	$ 7.51
Options exercised, Number of shares	(20,000)
Options exercised, Weighted Average Exercise Price	$ 13.09
Options forfeited, Number of Shares
Options forfeited, Weighted Average Exercise Price
Outstanding at March 31, 2013, Number of Shares	1,381,435
Outstanding at March 31, 2013, Weighted Average Exercise Price	$ 17.13
Maximum [Member]
Stock option activity
Outstanding at December 31, 2012, Option Price per Share	$ 25.91
Options granted, Option Price per Share	$ 16.59
Options exercised, Option Price per Share	$ 13.09
Options forfeited, Option Price per Share
Outstanding at March 31, 2013, Option Price per Share	$ 25.91
Minimum [Member]
Stock option activity
Outstanding at December 31, 2012, Option Price per Share	$ 12.60
Options granted, Option Price per Share	$ 16.59
Options exercised, Option Price per Share	$ 13.09
Options forfeited, Option Price per Share
Outstanding at March 31, 2013, Option Price per Share	$ 12.60