Stockholders' Equity (Details) (USD $)	3 Months Ended								12 Months Ended						12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Nov. 26, 2012 Maximum [Member]	Nov. 26, 2012 Minimum [Member]	Dec. 31, 2012 Series A Junior Participating Preferred Stock [Member]	Dec. 31, 2012 Dutch auction [Member]
Stockholders' Equity [Abstract]
Authorized number of shares to be repurchased (in shares)	14,500,000								14,500,000
Repurchase of treasury stock (in shares)									407,400	902,521
Shares withheld for tax withholding obligations for the vesting of restricted stock awards (in shares)									107,293	108,280
Remaining number of shares authorized to be repurchased (in shares)	829,472								829,472
Dividends declared per share of common stock (in dollars per share)	$ 0.17	$ 0.17	$ 0.17	$ 0.15	$ 0.15	$ 0.15	$ 0.15	$ 0.15
Special dividend declared (in dollars per share)	$ 1.00
Dividends paid									$ 42,728,000	$ 15,742,000	$ 13,527,000
Class of Stock [Line Items]
Range of price per share for tender offer												$ 31.00	$ 27.00
Preferred stock, authorized (in shares)	20,000,000				20,000,000				20,000,000	20,000,000				600,000
Max amount of dollars that could be used to purchase shares under tender offer															50,000,000
Repurchase of common stock (in shares)															80,983
Aggregate price paid related to tender offer shares repurchased									$ (3,162,000)						$ 3,200,000
Common stock purchase right per preferred stock share (in shares)									1