Stockholders' Equity (Details) (USD $)	0 Months Ended				1 Months Ended	6 Months Ended		12 Months Ended
	May 04, 2013	Nov. 30, 2012	Nov. 16, 2012	Feb. 21, 2012	Dec. 31, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Class of Stock [Line Items]
Payments of Dividends						$ 6,149,000	$ 0
Common Stock, Dividends, Per Share, Cash Paid	$ 0.125
Stock Repurchase Program, Authorized Amount			100,000,000
Treasury Stock, Shares, Acquired		256,262			873,146			1,129,408
Treasury Stock Acquired, Average Cost Per Share		$ 21.58			$ 24.26			$ 23.65
Stock Repurchase Program, Remaining Authorized Repurchase Amount		94,470,000			73,268,000
Gross proceeds from the issuance of common stock				225,000,000
Stock issued during period				6,122,000
Sale of stock, price per share				$ 36.75
Proceeds from sale of common stock, net of issuance costs						$ 0	$ 218,983,000
Common Stock, Dividends, Per Share, Declared	$ 0.50