Stockholders' Equity (Details) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended
	Feb. 14, 2013	Apr. 30, 2013	Mar. 31, 2013	Mar. 31, 2012
Components of basic and diluted earnings per share
Net income from continuing operations (in dollars)			$ 53,863,000	$ 46,837,000
Weighted average shares outstanding - basic			85,592,000	85,604,000
Dilutive potential shares from stock options			1,000	2,000
Weighted average shares outstanding - diluted			85,593,000	85,606,000
Earnings per share:
Earnings per share from continuing operations, basic and diluted (in dollars per share)			$ 0.63	$ 0.55
Anti-dilutive Securities
Anti-dilutive securities excluded from the diluted earnings per share (in shares)			0	0
Dividends
Dividends accrued, per share (in dollars per share)	$ 0.28		$ 0.28
Dividends to be paid (in dollars)			$ 24,000,000
Common stock repurchases
Shares repurchased in the open market or privately			81,701	366
Shares repurchased from employees to cover minimum income tax withholdings		464,177	2,601