Statements Of Changes In Shareholders' Equity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Balance	$ 363,390us-gaap_StockholdersEquity	$ 362,792us-gaap_StockholdersEquity	$ 322,206us-gaap_StockholdersEquity
Shares issued on exercise of options	89	2,598
Shares issued on exercise of options (in shares)	15,000	469,000
Cancellation of shares, value	(17,880)
Cancellation of shares, shares	(2,669,413)
Stock-based compensation expenses	309	1,536	547
Consolidated net income (loss)	(25,588)us-gaap_NetIncomeLoss	297us-gaap_NetIncomeLoss	66,921us-gaap_NetIncomeLoss
Cash dividends declared ($0.08 per share in 2014 and 2013, $0.28 per share in 2011)	(3,409)us-gaap_DividendsCash	(3,622)us-gaap_DividendsCash	(26,882)us-gaap_DividendsCash
Cash dividends reversal	41ntp_ReversalOfDividend
Cash dividends paid		(211)ntp_DividendsPaid
Balance	316,952us-gaap_StockholdersEquity	363,390us-gaap_StockholdersEquity	362,792us-gaap_StockholdersEquity
Parent Company
Condensed Financial Statements, Captions [Line Items]
Balance	363,390	362,792	322,206
Shares issued on exercise of options	89	2,598
Cancellation of shares, value	(17,880)
Stock-based compensation expenses	309	1,536	547
Consolidated net income (loss)	(25,588)	297	66,921
Cash dividends declared ($0.08 per share in 2014 and 2013, $0.28 per share in 2011)	(3,409)	(3,622)	(26,882)
Cash dividends reversal	41
Cash dividends paid		(211)
Balance	316,952	363,390	362,792
Common Stock
Condensed Financial Statements, Captions [Line Items]
Balance	453	448		448
Shares issued on exercise of options		5
Balance (in shares)	45,272,735	44,803,735		44,803,735
Shares issued on exercise of options (in shares)	15,000	469,000
Cancellation of shares, value	(27)
Cancellation of shares, shares	(2,669,413)
Balance	426	453		448
Balance (in shares)	42,618,322	45,272,735		44,803,735
Common Stock \| Parent Company
Condensed Financial Statements, Captions [Line Items]
Balance	453	448		448
Shares issued on exercise of options		5
Balance (in shares)	45,272,735	44,803,735		44,803,735
Shares issued on exercise of options (in shares)	15,000	469,000
Cancellation of shares, value	(27)
Cancellation of shares, shares	(2,669,413)
Balance	426	453		448
Balance (in shares)	42,618,322	45,272,735		44,803,735
Additional Paid-in Capital
Condensed Financial Statements, Captions [Line Items]
Balance	291,731	287,602	287,055
Shares issued on exercise of options	89	2,593
Cancellation of shares, value	(17,853)
Stock-based compensation expenses	309	1,536	547
Balance	274,276	291,731	287,602
Additional Paid-in Capital \| Parent Company
Condensed Financial Statements, Captions [Line Items]
Balance	291,731	287,602	287,055
Shares issued on exercise of options	89	2,593
Cancellation of shares, value	(17,853)
Stock-based compensation expenses	309	1,536	547
Balance	274,276	291,731	287,602
Retained Earnings
Condensed Financial Statements, Captions [Line Items]
Balance	71,214	74,750	34,711
Consolidated net income (loss)	(25,588)	297	66,921
Cash dividends declared ($0.08 per share in 2014 and 2013, $0.28 per share in 2011)	(3,409)	(3,622)	(26,882)
Cash dividends reversal	41
Cash dividends paid		(211)
Balance	42,258	71,214	74,750
Retained Earnings \| Parent Company
Condensed Financial Statements, Captions [Line Items]
Balance	71,214	74,750	34,711
Consolidated net income (loss)	(25,588)	297	66,921
Cash dividends declared ($0.08 per share in 2014 and 2013, $0.28 per share in 2011)	(3,409)	(3,622)	(26,882)
Cash dividends reversal	41
Cash dividends paid		(211)
Balance	42,258	71,214	74,750
Accumulated Other Comprehensive Loss
Condensed Financial Statements, Captions [Line Items]
Balance				(8)
Balance	(8)	(8)	(8)	(8)
Accumulated Other Comprehensive Loss \| Parent Company
Condensed Financial Statements, Captions [Line Items]
Balance				(8)
Balance	$ (8)	$ (8)	$ (8)	$ (8)

Amount of paid common stock dividends declared with the form of settlement in cash.

No definition available.

Name:	ntp_DividendsPaid
Namespace Prefix:	ntp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reversal of dividend.

+ References

No definition available.

+ Details

Name:	ntp_ReversalOfDividend
Namespace Prefix:	ntp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents the amount of recognized equity-based compensation related to stock options during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized).

+ References

No definition available.

+ Details

Name:	us-gaap_AdjustmentsToAdditionalPaidInCapitalShareBasedCompensationStockOptionsRequisiteServicePeriodRecognition
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_CondensedFinancialStatementsCaptionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of paid and unpaid cash dividends declared for classes of stock, for example, but not limited to, common and preferred.

+ References

+ Details

Name:	us-gaap_DividendsCash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Other Comprehensive Income

-URI http://asc.fasb.org/extlink&oid=6519514

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.19)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.18)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.22)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 19

-Article 5

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 20

-Article 9

+ Details

Name:	us-gaap_NetIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of shares issued which are neither cancelled nor held in the treasury.

+ References

No definition available.

+ Details

Name:	us-gaap_SharesOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 4.E)

-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74512-122707

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 4

-Section E

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.29-31)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30, 31

-Article 5

+ Details

Name:	us-gaap_StockholdersEquity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of share options (or share units) exercised during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28,29)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(1)(iv)(2)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Value of stock issued as a result of the exercise of stock options.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.29-31)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30, 31

-Article 5

+ Details

Name:	us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of shares that have been repurchased and retired during the period.

+ References

+ Details

Name:	us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

+ References

+ Details

Name:	us-gaap_StockRepurchasedAndRetiredDuringPeriodValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=us-gaap_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedOtherComprehensiveIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_AdditionalPaidInCapitalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_RetainedEarningsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: