Business Segments (Data by Geographic Region) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 284,218	$ 220,792	$ 178,007	$ 173,421	$ 286,519	$ 239,107	$ 196,500	$ 193,734	$ 856,438	$ 915,860	$ 896,782
Long-lived assets	162,104				157,182				162,104	157,182	187,896
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									737,448	795,071	779,890
Long-lived assets	157,022				151,618				157,022	151,618	182,116
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									118,990	120,789	116,892
Long-lived assets	$ 5,082				$ 5,564				$ 5,082	$ 5,564	$ 5,780