Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Jan. 01, 2018
Summary Of Significant Accounting Policies [Line Items]
Aggregate amount of transaction price allocated to remaining performance obligations	$ 517,000
Remaining performance obligations expected to be recognized, year	2023
Restricted cash	$ 2,700		$ 4,200
Proceeds from sale/maturity of short-term investments	$ 79,508	$ 37,782
80% of Remaining Performance Obligations Amount Over Next Three Years
Summary Of Significant Accounting Policies [Line Items]
Remaining performance obligations expected to be recognized, percentage	80.00%
Remaining performance obligations expected to be recognized, period	3 years
Minimum
Summary Of Significant Accounting Policies [Line Items]
Billed accounts receivable, payment term	30 days
Maximum
Summary Of Significant Accounting Policies [Line Items]
Billed accounts receivable, payment term	60 days
Short-term investment contractual maturities	2 years		2 years
Cloud and Related Solutions Revenue | Minimum
Summary Of Significant Accounting Policies [Line Items]
Long-term arrangements service period	3 years
Future revenue including variable consideration, contractual terms ending, year	2019
Cloud and Related Solutions Revenue | Maximum
Summary Of Significant Accounting Policies [Line Items]
Long-term arrangements service period	5 years
Future revenue including variable consideration, contractual terms ending, year	2023
ASU 606
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect upon adoption of new accounting principle, increase in retained earnings net of tax				$ 7,000