Capital Stock - Narrative (Details) - USD ($) $ in Thousands	6 Months Ended		227 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Dec. 31, 2016
Equity [Abstract]
Shares repurchased (shares)	3,000,000		32,900,000
Shares authorized for repurchase (shares)	40,000,000		40,000,000
Treasury stock repurchases	$ 68,255	$ 0	$ 456,600
Shares retired (shares)			20,000,000
Treasury stock (shares)	12,935,926		12,935,926	9,892,680