Capital Stock - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Apr. 30, 2018	Feb. 28, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Equity [Abstract]
Incremental shares authorized		25,000,000
Treasury stock			23,263,707		14,935,926
Shares authorized for repurchase		30,100,000
Remaining shares available for repurchase (in shares)			21,700,000
Subsequent Event [Line Items]
Shares repurchased			8,300,000
Treasury stock repurchases (in usd)			$ 207,134	$ 0
Subsequent Event
Subsequent Event [Line Items]
Shares repurchased	1,600,000
Treasury stock repurchases (in usd)	$ 38,500