Commitments and Contingencies - Narrative (Details) - USD ($)			1 Months Ended	12 Months Ended
	Jun. 20, 2017	Aug. 26, 2016	Aug. 31, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Long-term Purchase Commitment [Line Items]
Lease term			120 months
Recorded assets				$ 143,299,000	$ 126,093,000
Lease financing obligation				39,600,000	41,200,000
Lease financing obligation, current				1,900,000
Lease financing obligations, non-current				37,673,000	39,593,000
Non-cancelable purchase commitments				195,100,000
Cisco Systems, Inc.
Long-term Purchase Commitment [Line Items]
Minimum monetary sanction for violation of cease and desist order		$ 100,000.00
Civil penalty	$ 307,000,000
USITC
Long-term Purchase Commitment [Line Items]
Minimum monetary sanction for violation of cease and desist order				100,000.00
Civil penalty				307,000,000
Other Assets
Long-term Purchase Commitment [Line Items]
Restricted deposits				36,900,000	63,100,000
Contract with manufacturers and suppliers
Long-term Purchase Commitment [Line Items]
Non-cancelable purchase commitments				147,900,000
Building and improvements
Long-term Purchase Commitment [Line Items]
Recorded assets				53,400,000	53,400,000
Land
Long-term Purchase Commitment [Line Items]
Lease expense under financing obligation				1,300,000	$ 1,300,000	$ 1,300,000
Line of Credit
Long-term Purchase Commitment [Line Items]
Letter of credit				$ 4,000,000