Revenue Disaggregated Revenue by Geography (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 327,169,000	$ 343,236,000	$ 1,059,662,000	$ 922,489,000
EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenues	30,759,000	31,034,000	104,150,000	87,892,000
Asia Pacific [Member]
Disaggregation of Revenue [Line Items]
Revenues	17,779,000	16,982,000	54,813,000	44,071,000
Latin America [Member]
Disaggregation of Revenue [Line Items]
Revenues	16,051,000	16,349,000	44,701,000	42,034,000
North America [Member]
Disaggregation of Revenue [Line Items]
Revenues	17,739,000	21,939,000	54,684,000	50,037,000
Other foreign countries [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	120,000	80,000	120,000
Foreign [Member]
Disaggregation of Revenue [Line Items]
Revenues	82,328,000	86,424,000	258,428,000	224,154,000
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenues	$ 244,841,000	$ 256,812,000	$ 801,234,000	$ 698,335,000