Restructuring (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Expected restructuring charge	$ 65,000
Restructuring charges recognized	49,300	$ 9,700
Restructuring Reserve [Roll Forward]
Balance	1,613	387	$ 281
Costs incurred	54,884	10,301	767
Cash disbursements	(9,110)	(4,488)	(661)
Restructuring-related software charges	(33,144)	(4,587)
Balance	14,243	1,613	387
Employee Severance and Related Benefits
Restructuring Reserve [Roll Forward]
Balance	1,444	162	0
Costs incurred	17,311	5,714	767
Cash disbursements	(5,898)	(4,432)	(605)
Restructuring-related software charges	0	0
Balance	12,857	1,444	162
Software Charges
Restructuring Reserve [Roll Forward]
Balance	0	0	0
Costs incurred	31,965	4,587	0
Cash disbursements	0	0	0
Restructuring-related software charges	(31,965)	(4,587)
Balance	0	0	0
Excess Facilities, Contract Terminations and Other
Restructuring Reserve [Roll Forward]
Balance	169	225	281
Costs incurred	5,608	0	0
Cash disbursements	(3,212)	(56)	(56)
Restructuring-related software charges	(1,179)	0
Balance	$ 1,386	$ 169	$ 225