Capital Stock - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended				3 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 02, 2016	Feb. 26, 2016	Feb. 22, 2016	Oct. 31, 2018	Jul. 31, 2018	Feb. 28, 2018	Jan. 31, 2018	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 30, 2018	May 01, 2014
Incentive Plans
Issuance of common stock (in shares)		6,600,000.0		44,000,000
Share price (in usd per share)				$ 19.675
Sale of common stock, net		$ 129,900	$ 865,700							$ 0	$ 0	$ 995,279
Incremental shares approved for repurchase (in shares)						20,000,000	25,000,000
Treasury stock, number of shares authorized to be repurchased										11,600,000
Number of shares repurchased										38,500,000.0	5,000,000.0	0
Cost of shares repurchased										$ 904,100	$ 123,700
Cumulative number of shares repurchased under a share repurchase program										73,400,000
Treasury stock, cumulative shares retired										20,000,000
Cumulative cost of shares repurchased under a share repurchase program										$ 1,400,000
Treasury stock reissued										0
Shares held as treasury stock (in shares)	14,935,926									53,409,705	14,935,926		1,379,268
Cash dividends, per share (in dollars per share)	$ 0.05				$ 0.07			$ 0.06	$ 0.06	$ 0.25	$ 0.17	$ 0.08
2014 Incentive Plan
Incentive Plans
Number of shares reserved for issuance														18,000,000
Number of shares available for issuance										13,700,000
2014 Incentive Plan | Stock options | Maximum
Incentive Plans
Number of shares reserved for issuance														10,000,000