Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2016
Class of Stock [Line Items]
Dividends paid		$ 106,943	$ 101,511	$ 205,468
Amount paid for repurchase of common stock		$ 29,100	$ 46,957	$ 83,593
Treasury
Class of Stock [Line Items]
Repurchased shares		1,205,790	1,841,800	3,053,204
Amount paid for repurchase of common stock		$ 29,100	$ 46,957	$ 83,593
Class B
Class of Stock [Line Items]
Number of shares authorized under share repurchase program					4,000,000.0
Remaining number of shares authorized to be repurchased		1,000,000
Special Dividend
Class of Stock [Line Items]
Dividends paid	$ 102,200
Common stock, dividends, per share, cash paid (usd per share)	$ 1