Subsequent Event (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 22, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 13, 2018	Feb. 15, 2017
Subsequent Event [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired		$ 20,000	$ 0	$ 0
Stock Repurchase Program, Authorized Amount						$ 100,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	$ 37,000
Stock Repurchase Program, Authorized Amount					$ 100,000