Summary of Carrying Amounts and Estimated Fair Values of Other Financial Instruments (Detail) (USD $) In Thousands	Sep. 30, 2011
Liabilities:
Derivative liabilities	$ 11,900
7 1/4% Senior Notes | Carrying Amount
Liabilities:
Long term debt fair value	245,025
Carrying Amount
Assets:
Cash and cash equivalents	140,465
Carrying Amount | Bank debt
Liabilities:
Long term debt fair value	1,185,925
Carrying Amount | Interest rate swap agreements
Liabilities:
Derivative liabilities	11,593
Carrying Amount | Natural gas swap agreements
Liabilities:
Derivative liabilities	328
7 1/4% Senior Notes | Fair Value
Liabilities:
Long term debt fair value	263,750
Fair Value
Assets:
Cash and cash equivalents	140,465
Fair Value | Bank debt
Liabilities:
Long term debt fair value	1,185,925
Fair Value | Interest rate swap agreements
Liabilities:
Derivative liabilities	11,593
Fair Value | Natural gas swap agreements
Liabilities:
Derivative liabilities	$ 328