Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

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Amount of cash inflow (outflow) from operating activities, including discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

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The cumulative amount of the reporting entity's undistributed earnings or deficit.

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Description of timing for satisfying performance obligation in contract with customer. Includes, but is not limited to, as services are rendered, and upon shipment, delivery or completion of service.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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Application of Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total stockholder’s equity	$ 1,991,163	$ 2,260,897		$ 2,449,589	$ 2,012,321
Retained earnings	1,173,517			1,051,792
Cash flows from operating	316,452	699,942
Cash flows from investing	(357,630)	(1,327,696)
Cash flows from financing	$ 35,749	629,928
Expected life of customer contract	The primary impact of ASC 606 to the Company relates to the accounting for certain contract costs and contract fulfillment costs, which were expensed as incurred under ASC 605. Under ASC 606, these costs are deferred and amortized over the expected life of the customer contract, which the Company determined to be 10 years.
Retained earnings
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total stockholder’s equity	$ 1,173,517	892,058			$ 906,122
ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total stockholder’s equity				2,482,541
ASC 606 \| Retained earnings
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total stockholder’s equity				1,084,744
ASC 606 \| Difference between revenue guidance in effect before and after ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total stockholder’s equity				32,952
Retained earnings			$ 32,952
ASC 606 \| Difference between revenue guidance in effect before and after ASC 606 \| Retained earnings
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total stockholder’s equity				$ 32,952
ASU 2016-15, COLI
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash flows from operating		1,680
Cash flows from investing		1,680
ASU 2016-15, Due to / from parent and affiliate
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Cash flows from operating		21,388
Cash flows from financing		$ 9,760