Basis of Presentation (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Cash and cash equivalents	$ 251,741		$ 255,139
Restricted cash	$ 304		$ 304
Federal statutory tax rate	21.00%		35.00%
Defined Benefit Plan Net Periodic Benefit Cost		$ 400
Other Expense [Member] \| Adjustments for New Accounting Pronouncement [Member]
Defined Benefit Plan Net Periodic Benefit Cost		$ 200
Retained Earnings (Accumulated Deficit) [Member]
Tax cuts and Jobs Act, reclassification tax effect			$ 4,468
Accumulated Other Comprehensive Loss [Member]
Tax cuts and Jobs Act, reclassification tax effect			$ (4,468)

Tax cuts and job act of 2017 reclassification from AOCI to retained earnings, tax effect.

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

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-Publisher FASB
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- Definition

Amount of net periodic benefit cost (credit) for defined benefit plan.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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- Definition

Amount of cash restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

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