Stock Repurchase Program (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 16, 2014	Mar. 08, 2012	May. 02, 2011
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program authorized amount						$ 257,800	$ 323,700	$ 300,000
Treasury stock value acquired cost method			$ 112,415	$ 92,436
Stock repurchase program remaining authorized repurchase amount	$ 306,200		$ 306,200		$ 400,000	$ 400,000
Stock Repurchase Program [Member]
Equity, Class of Treasury Stock [Line Items]
Treasury stock shares acquired	0	1,500,000	1,700,000	1,500,000
Treasury stock value acquired cost method		$ 69,000	$ 93,800	$ 69,000