Restructuring and Related Charges (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Consulting and Other Costs [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges				$ 200
2015 Restructuring Plan [Member]
Restructuring Reserve [Roll Forward]
Accrued restructuring and related charges liability as of period start		$ 4,305		9,993
Restructuring charges				8,729		$ 15,097
Payments		(1,445)		(14,381)		(2,999)
Non-cash charges	[1]			(67)		(2,105)
Non-cash charges	[1]			67		2,105
Adjustments	[2]			(103)
Accrued restructuring and related charges liability as of period end		2,860		4,305		9,993
Restructuring Cost [Abstract]
Restructuring charges incurred						24,000
2015 Restructuring Plan [Member] | Severance and Other Employee-related Costs [Member]
Restructuring Reserve [Roll Forward]
Accrued restructuring and related charges liability as of period start		4,242		7,093
Restructuring charges				4,599		8,836
Payments		(1,434)		(7,414)		(825)
Non-cash charges	[1]			(67)		(918)
Non-cash charges	[1]			67		918
Adjustments	[2]			(103)
Accrued restructuring and related charges liability as of period end		2,808		4,242		7,093
2015 Restructuring Plan [Member] | Consulting and Other Costs [Member]
Restructuring Reserve [Roll Forward]
Accrued restructuring and related charges liability as of period start	[3]	63		2,900
Restructuring charges	[3]			4,130		5,074
Payments	[3]	(11)		(6,967)		(2,174)
Non-cash charges	[1],[3]			0		0
Non-cash charges	[1],[3]			0		0
Adjustments	[2],[3]			0
Accrued restructuring and related charges liability as of period end	[3]	52		63		2,900
2015 Restructuring Plan [Member] | Asset Retirements [Member]
Restructuring Reserve [Roll Forward]
Accrued restructuring and related charges liability as of period start		0		0
Restructuring charges				0		1,187
Payments		0		0		0
Non-cash charges	[1]			0		(1,187)
Non-cash charges	[1]			0		1,187
Adjustments	[2]			0
Accrued restructuring and related charges liability as of period end		0		0		0
2016 Restructuring Plan [Member]
Restructuring Reserve [Roll Forward]
Accrued restructuring and related charges liability as of period start		3,899
Restructuring charges		811		4,933
Payments		(3,463)		(747)
Non-cash charges		(159)	[4]	(287)	[5]
Non-cash charges		159	[4]	287	[5]
Accrued restructuring and related charges liability as of period end		1,088		3,899
Restructuring Cost [Abstract]
Restructuring charges incurred				5,600
2016 Restructuring Plan [Member] | Severance and Other Employee-related Costs [Member]
Restructuring Reserve [Roll Forward]
Accrued restructuring and related charges liability as of period start		3,851
Restructuring charges		795		4,697
Payments		(3,399)		(559)
Non-cash charges		(159)	[4]	(287)	[5]
Non-cash charges		159	[4]	287	[5]
Accrued restructuring and related charges liability as of period end		1,088		3,851
2016 Restructuring Plan [Member] | Consulting and Other Costs [Member]
Restructuring Reserve [Roll Forward]
Accrued restructuring and related charges liability as of period start	[6]	48
Restructuring charges	[6]	16		236
Payments	[6]	(64)		(188)
Non-cash charges	[6]	0	[4]	0	[5]
Non-cash charges	[6]	0	[4]	0	[5]
Accrued restructuring and related charges liability as of period end	[6]	0		$ 48
2017 Restructuring Plan [Member]
Restructuring Cost [Abstract]
Restructuring charges incurred		2,600
2017 Restructuring Plan [Member] | Severance and Other Employee-related Costs [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges		2,571
Payments		(540)
Non-cash charges	[5]	(108)
Non-cash charges	[5]	108
Accrued restructuring and related charges liability as of period end		$ 1,923
Lease Termination Costs [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges						$ 400

[1] Non-cash charges consist primarily of share-based compensation costs as well as asset retirements.

[2] Adjustments resulted primarily from actual employee tax and benefit amounts differing from previous estimates.

[3] Consulting and other costs primarily consist of third-party consulting charges. Consulting and other costs also include approximately $0.2 million and $0.4 million of lease termination costs in 2016 and 2015, respectively.

[4] Adjustments consist primarily of actual employee tax and benefit amounts differing from previous estimates.

[5] Non-cash charges consist of share-based compensation costs.

[6] Consulting and other costs consist of third-party consulting charges.