Stock Repurchase Program (Details) (USD $)	0 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 08, 2012	May 02, 2011	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Equity, Class of Treasury Stock [Line Items]
Treasury stock value acquired cost method					$ 85,496,000	$ 33,143,000
2011 Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount	323,700,000	300,000,000
Treasury stock shares acquired			0	562,000	2,700,000	562,000
Treasury stock value acquired cost method				13,900,000	70,000,000	13,900,000
Stock repurchase program remaining authorized repurchase amount					$ 280,000,000		$ 350,000,000