Earnings Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010		Sep. 30, 2011	Sep. 30, 2010
Conversion price of convertible notes	$ 31.25			$ 31.25
Net income	$ 29,439	$ 20,164	[1]	$ 64,022	$ 57,129	[1]
Weighted average number of common shares outstanding - basic	40,182	45,471		41,535	45,708
Effect of dilutive stock options	884	803		895	947
Effect of dilutive convertible notes	647	449		722	950
Effect of dilutive restricted shares	554	258		519	285
Weighted average number of common shares outstanding - diluted	42,267	46,981		43,671	47,890
Earnings per common share - basic	$ 0.73	$ 0.44	[1]	$ 1.54	$ 1.25	[1]
Earnings per common share - diluted	$ 0.70	$ 0.43	[1]	$ 1.47	$ 1.19	[1]
Antidilutive stock options and restricted shares	2,612	2,059		2,330	1,671
3 3 /4% Senior Subordinated Convertible Notes Due 2012 [Member]
Senior subordinated convertible notes, interest percentage	3.75%			3.75%
Debt maturity period				2012

[1] As Revised (Note 2)