Common Stock - Narrative (Details) - USD ($)	6 Months Ended	12 Months Ended
	Dec. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2015	Jun. 08, 2017	Aug. 29, 2016	Apr. 26, 2016	Jan. 22, 2015
Common Stock
Approved stock repurchase program, authorized amount					$ 200,000,000		$ 400,000,000	$ 450,000,000
Repurchase of common stock (in shares)		5,185,257	4,750,692	7,731,428
Repurchase of common stock, amount		$ 375,000,000	$ 180,066,000	$ 298,344,000
Remaining capacity under the stock repurchase program		$ 346,300,000
Accelerated Share Repurchase Program [Member]
Common Stock
Accelerated Share Repurchases, Settlement (Payment) or Receipt						$ (100,000,000)
Repurchase of common stock (in shares)	2,100,000	2,106,709
Repurchase of common stock, amount		$ 100,000,000
Open Market Transaction [Member]
Common Stock
Repurchase of common stock, amount		$ 275,000,000