Common Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common stock repurchases, value	$ 138,275	$ 40,791	$ 20,520
Common Stock
Class of Stock [Line Items]
Treasury shares issued (in shares)	0	0	0
Employee stock plans (in shares)	332,893	341,837	621,259
Treasury Stock
Class of Stock [Line Items]
Common stock repurchases (in shares)	2,292,100	677,100	550,994
Common stock repurchases, value	$ 138,275	$ 40,791	$ 20,520
Employee stock plans (in shares)	86,000	89,000	132,000