Shareholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended		3 Months Ended		6 Months Ended		1 Months Ended		6 Months Ended
	Jul. 31, 2013	Apr. 30, 2013	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jul. 31, 2013 2013 Stock Repurchase Program	Jan. 31, 2013 2013 Stock Repurchase Program	Jun. 30, 2013 2013 Stock Repurchase Program
Number of shares authorized to be repurchased under the current open-market stock repurchase program								10,000,000
Repurchase of stock program, period								2 years
Number of shares repurchased under the current open-market stock repurchase program							669,054		2,466,658
Payments for shares repurchased under the current open-market stock repurchase program (in dollars)					$ 181,108	$ 201,020	$ 51,904		$ 181,108
Remaining number of shares authorized to be repurchased under the current open-market stock repurchase program							6,864,288
Quarterly dividend approved by Board prior to payment, per share (in dollars per share)	$ 0.20	$ 0.105
Dividend paid (in dollars)			16,756	17,048	16,756	19,500
Dividends declared			$ 16,713	$ 16,889	$ 33,468	$ 33,938