Share Repurchases (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share Repurchases
Share repurchase program amount authorized	$ 10,000
Shares repurchased (in shares)	3,086	0	0	50,068
Weighted average price per share (in dollars per share)	$ 54.79			$ 53.52
Shares paid for tax withholding for share-based compensation		5,385
Weighted average per share prices for shares used to pay tax withholding liability (in dollars per share)		$ 76.32