Revenue from Contracts with Customers (Details 4) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
ASSETS
Accounts receivable, net	$ 54,240	$ 77,087	$ 81,397
Contract assets	2,362	4,720	0
Other current assets	2,536	4,273	3,900
Other assets	6,591	4,248	3,230
LIABILITIES
Deferred revenue and related expenses	6,034	5,906	5,342
Deferred income taxes	0	892	773
Other current liabilities	3,564	3,977	3,732
Other long-term liabilities	4,060	4,503	4,201
STOCKHOLDERS’ EQUITY
Retained earnings	812,704	795,154	794,583
Total assets	125,175		130,812
Liabilities	134,636		165,447
Calculated under Revenue Guidance in Effect before Topic 606
ASSETS
Accounts receivable, net			81,397
Contract assets			0
Other current assets			3,900
Other assets			3,230
LIABILITIES
Deferred revenue and related expenses			5,342
Deferred income taxes			773
Other current liabilities			3,732
Other long-term liabilities			4,201
STOCKHOLDERS’ EQUITY
Retained earnings			$ 794,583
Cumulative Adjustments | Accounting Standards Update 2014-09
ASSETS
Accounts receivable, net		(4,310)
Contract assets		4,720
Other current assets		373
Other assets		1,018
LIABILITIES
Deferred revenue and related expenses		564
Deferred income taxes		119
Other current liabilities		245
Other long-term liabilities		302
STOCKHOLDERS’ EQUITY
Retained earnings	1,300	$ 571
Total assets	1,800
Liabilities	$ 500