Revenue from Contracts with Customers (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	$ (5,248,991)		$ (5,248,991)			$ (5,229,584)
Income before income taxes	53,464	$ 42,251	$ 114,753	$ 126,757
Advanced billings, revenue recognized	$ 128,000
Expected timing of satisfaction period	12 months		12 months
Selling, general and administrative expense
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Amortization expense	$ 3,000		$ 7,000
Other assets
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Unamortized contract costs	26,000		26,000
Software
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cost of products and sales	26,459	$ 23,361	50,514	$ 46,515
ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings					$ 9,000
ASC 606 | Total increase (decrease)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	(7,167)		(7,167)
Income before income taxes	11,025		20,532
ASC 606 | Software
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cost of products and sales	10,000		21,000
ASC 606 | Software | Total increase (decrease)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cost of products and sales	690		1,972
Income before income taxes	$ 9,000		$ 19,000