Fair value portion 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.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

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- Definition

Fair value of all liability derivatives designated as cash flow hedging instruments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624163-113959

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

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

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

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Summary of Carrying Amounts and Estimated Fair Values of Other Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Sep. 09, 2013	Mar. 23, 2012
Carrying Amount
Assets:
Cash and cash equivalents	$ 222,591	$ 160,463
Carrying Amount \| Interest rate swap agreements
Liabilities:
Derivative liabilities	1,196	6,895
Carrying Amount \| Natural gas swap agreements
Liabilities:
Derivative liabilities	746	22
Fair Value
Assets:
Cash and cash equivalents	222,591	160,463
Fair Value \| Interest rate swap agreements
Liabilities:
Derivative liabilities	1,196	6,895
Fair Value \| Natural gas swap agreements
Liabilities:
Derivative liabilities	746	22
Senior Notes [Member] \| 5½% Senior Notes [Member]
Liabilities:
Stated interest rate			5.50%
Senior Notes [Member] \| 5% Senior Notes due 2020 [Member]
Liabilities:
Stated interest rate				5.00%
Senior Notes [Member] \| Carrying Amount \| 5½% Senior Notes [Member]
Liabilities:
Long term debt fair value	300,000	300,000
Senior Notes [Member] \| Carrying Amount \| 5% Senior Notes due 2020 [Member]
Liabilities:
Long term debt fair value	500,000	500,000
Senior Notes [Member] \| Fair Value \| 5½% Senior Notes [Member]
Liabilities:
Long term debt fair value	307,500	298,125
Senior Notes [Member] \| Fair Value \| 5% Senior Notes due 2020 [Member]
Liabilities:
Long term debt fair value	500,715	495,625
Bank Borrowings [Member] \| Carrying Amount
Liabilities:
Long term debt fair value	798,963	903,836
Bank Borrowings [Member] \| Fair Value
Liabilities:
Long term debt fair value	$ 798,963	$ 903,836