Earnings per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Earnings Per Share [Abstract]
Net income for basic and diluted earnings per share	$ 18,072	$ 16,536	$ 51,824	$ 54,048
Basic weighted average shares outstanding	37,214	37,345	36,859	38,215
Dilutive effect of stock options and restricted stock awards	1,906	3,104	2,299	3,185
Diluted weighted average shares outstanding	39,120	40,449	39,158	41,400
Basic earnings per common share	$ 0.49	$ 0.44	$ 1.41	$ 1.41
Diluted earnings per common share	$ 0.46	$ 0.41	$ 1.32	$ 1.31