Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended
	Nov. 02, 2018	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2017
Subsequent events
Cost of shares repurchased		$ 2,016	$ 3,626
2004 Stock Repurchase Program
Subsequent events
Shares authorized under repurchase program				1,000,000
Shares available for repurchase		900,000
Subsequent event | 2004 Stock Repurchase Program
Subsequent events
Shares available for repurchase	548,800
Number of shares repurchased	351,200
Cost of shares repurchased	$ 23,100
Subsequent event | 2004 Stock Repurchase Program | Weighted average
Subsequent events
Share Price	$ 65.69