Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2012

Benefit Plans [Abstract]

Schedule of option activity and options exercisable including the weighted average exercise price

	Year Ended December 31,
	2012					2011					2010
	Shares			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price
Options outstanding at January 1,		3,086,019		$	23.52		3,344,450		$	22.80		3,504,319		$	22.09
Options granted during the year		128,500			29.63		160,600			27.41		282,000			23.72
Options exercised during the year		(327,498	)		17.95		(309,447	)		17.19		(422,069	)		17.78
Options terminated during the year		(48,468	)		27.63		(109,584	)		25.01		(19,800	)		22.03
Options outstanding at December 31,		2,838,553			24.37		3,086,019			23.52		3,344,450			22.80
Options exercisable at December 31,		2,322,258			24.64		2,306,159			24.43		2,148,100			23.91

Options outstanding and options exercisable by exercise price with the weighted average remaining contractual life for the options outstanding and the weighted average exercise price

	Options Outstanding						Options Exercisable
Exercise Price	Number Outstanding at December 31, 2012		Weighted Average Remaining Contractual Life (Years)		Weighted Average Exercise Price		Number Exercisable at December 31, 2012		Weighted Average Exercise Price
$10–15		20,000		0.25	$	11.74		20,000	$	11.74
15–20		420,608		2.86		15.65		265,608		15.67
20–25		1,161,150		2.57		21.73		1,008,275		21.55
25–30		688,295		3.61		28.93		575,375		29.81
30–35		548,500		2.03		31.39		453,000		31.39
10–35		2,838,553		2.74		24.37		2,322,258		24.64

Summary of activity of the Company's restricted stock units

	Year Ended December 31,
	2012					2011
	Number of Shares			Weighted Average Grant Date Fair Value		Number of Shares			Weighted Average Grant Date Fair Value
Restricted stock unvested as of January 1,		187,810		$	26.33		110,200		$	23.61
Restricted stock granted during the year		109,200			31.37		125,800			27.99
Restricted stock vested during the year		(34,190	)		27.85		(39,105	)		23.91
Restricted stock forfeited during the year		—			—		(9,085	)		25.36
Restricted stock unvested as of December 31,		262,820			28.22		187,810			26.33