Share repurchases Share Repurchase Tender Offer (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock (in shares)	30,592	32,652
Value of treasury stock acquired	$ 1,747,968	$ 1,860,157
Treasury stock acquired, average cost per share	$ 57.14	$ 56.97
Tender Offer
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock (in shares)	21,802	21,802
Value of treasury stock acquired	$ 1,233,886	$ 1,233,886
Treasury stock acquired, average cost per share	$ 56.60	$ 56.60
Treasury Stock, Shares Repurchases, Table Footnotes:
Treasury Stock Acquired, Average Cost Per Share, Clearing Price	$ 56.50	$ 56.50
Share Repurchase Fees And Expenses	$ 2,074	$ 2,074
Open Market Purchases
Equity, Class of Treasury Stock [Line Items]
Repurchase of common stock (in shares)	8,790	10,850
Value of treasury stock acquired	$ 514,082	$ 626,271
Treasury stock acquired, average cost per share	$ 58.49	$ 57.72