Stockholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stockholders' Equity [Abstract]
Authorized number of shares to be repurchased (in shares)	14,500,000								14,500,000
Shares repurchased under the program (in shares)									902,521	271,739
Shares withheld for tax withholding obligations for the vesting of restricted stock awards (in shares)									108,280	97,419
Remaining number of shares authorized to be repurchased (in shares)	1,236,872								1,236,872
Dividends declared per share of common stock (in dollars per share)	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.13	$ 0.13	$ 0.13	$ 0.13
Dividends paid									$ (15,742)	$ (13,527)	$ (13,272)
Class of Stock [Line Items]
Preferred stock, authorized (in shares)	20,000,000				20,000,000				20,000,000	20,000,000	20,000,000
Series A Junior Participating Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, authorized (in shares)	600,000				600,000				600,000	600,000	600,000