Stockholders' Equity (Details) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended
	Jul. 18, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Components of basic and diluted earnings per share
Net income from continuing operations		$ 52,116,000	$ 39,371,000	$ 140,178,000	$ 132,836,000
Weighted average shares outstanding - basic		85,753,000	85,776,000	85,817,000	85,951,000
Dilutive potential shares from stock options		2,000	6,000	2,000	13,000
Weighted average shares outstanding - diluted		85,755,000	85,782,000	85,819,000	85,964,000
Earnings per share:
Basic (in dollars per share)		$ 0.61	$ 0.46	$ 1.63	$ 1.55
Diluted (in dollars per share)		$ 0.61	$ 0.46	$ 1.63	$ 1.55
Dividends
Dividends accrued, per share (in dollars per share)	$ 0.25			$ 0.75
Dividends to be paid (in dollars)		$ 21,400,000		$ 21,400,000
Common stock repurchases
Shares repurchased in the open market or privately		213,366	651,878	1,158,720	1,609,551
Shares repurchased from employees to cover their minimum income tax withholdings		1,966	1,355	415,320	341,527
Anti-dilutive Securities
Anti-dilutive securities excluded from the diluted earnings per share (in shares)			27,000