Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
Apr. 05, 2015	Mar. 30, 2014
Cash flows from operating activities:
Net earnings	$ 8,109us-gaap_NetIncomeLoss	$ 4,690us-gaap_NetIncomeLoss
Adjustments to reconcile net earnings to net cash provided by operating activities, net of acquisition related assets:
Provision for depreciation	2,485us-gaap_Depreciation	2,337us-gaap_Depreciation
Intangibles amortization	2,394us-gaap_AmortizationOfIntangibleAssets	2,443us-gaap_AmortizationOfIntangibleAssets
Provision for doubtful accounts	6us-gaap_ProvisionForDoubtfulAccounts	180us-gaap_ProvisionForDoubtfulAccounts
Noncash retirement plan expense	231npk_NoncashRetirementPlanExpense
Other	38us-gaap_OtherNoncashIncomeExpense	32us-gaap_OtherNoncashIncomeExpense
Changes in:
Accounts receivable	17,400	22,886
Inventories	(4,171)us-gaap_IncreaseDecreaseInInventories	1,597us-gaap_IncreaseDecreaseInInventories
Other current assets	(8,737)	3
Accounts payable and accrued liabilities	(1,194)	(8,402)
Federal and state income taxes	6,256	(1,293)
Net cash provided by operating activities	22,817	24,473
Cash flows from investing activities:
Marketable securities purchased	(2,015)	(1,208)
Marketable securities - maturities and sales	3,838	9,912
Purchase of property, plant and equipment	(1,553)	(3,868)
Acquisition of businesses, net of cash acquired		(10,000)
Sale of property, plant and equipment	22	300
Net cash provided by (used in) investing activities	292	(4,864)
Cash flows from financing activities:
Dividends paid	(28,114)us-gaap_PaymentsOfDividendsCommonStock	(34,954)us-gaap_PaymentsOfDividendsCommonStock
Proceeds from sale of treasury stock	323us-gaap_ProceedsFromSaleOfTreasuryStock	362us-gaap_ProceedsFromSaleOfTreasuryStock
Other	(5)
Net cash used in financing activities	(27,796)	(34,592)
Net decrease in cash and cash equivalents	(4,687)	(14,983)
Cash and cash equivalents at beginning of year	54,043	22,953
Cash and cash equivalents at end of year	$ 49,356	$ 7,970

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