Capital Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		1 Months Ended		3 Months Ended
	Mar. 13, 2019	Apr. 30, 2019	Feb. 28, 2018	Mar. 31, 2019	Mar. 31, 2018
Dividends per Share [Abstract]
Payment of cash dividends				$ 20,531	$ 19,801
Repurchases of Common Stock [Abstract]
Class A common stock repurchased				825	$ 17,386
Amount available for repurchases				$ 470,200
Treasury Stock [Member]
Repurchases of Common Stock [Abstract]
Class A common stock repurchased (in shares)				14	200
Class A common stock repurchased				$ 825	$ 17,386
Dividend Declared 2019 Q1 [Member]
Dividends per Share [Abstract]
Dividend payable, date declared				2019-02
Dividend payable per share (in dollars per share)			$ 0.37
Payment of cash dividends	$ 20,500
Dividend payable, date paid				Mar. 13, 2019
Dividend payable, date of record				Feb. 25, 2019
Dividend Declared 2019 Q2 [Member] | Subsequent Event [Member]
Dividends per Share [Abstract]
Dividend payable, date declared		2019-04
Dividend payable per share (in dollars per share)		$ 0.37
Dividend payable, date paid		Jun. 12, 2019
Dividend payable, date of record		May 31, 2019
Stock Options [Member]
Net Income per Share [Abstract]
Anti-dilutive shares excluded from calculation of diluted earnings per share (in shares)				1,000	900