Benefit Obligations - Fair Value of Assets for Defined Benefit Pension Plans by Asset Category (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	$ 993,231		$ 867,241
Pension Benefits [Member] | Cash and Cash Equivalents [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	23,687		28,676
Pension Benefits [Member] | Domestic Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	183,538		169,994
Pension Benefits [Member] | International Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	94,155		78,603
Pension Benefits [Member] | US Treasury Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	61,173		80,426
Pension Benefits [Member] | Corporate Bond Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	248,680		155,666
Pension Benefits [Member] | Asset-backed and mortgage-backed securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	3,848		2,976
Pension Benefits [Member] | Municipal Bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	12,818		6,334
Pension Benefits [Member] | Government Bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	30,521		17,242
Pension Benefits [Member] | Commingled funds - equities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	194,302		163,510
Pension Benefits [Member] | Commingled funds - bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	139,954		156,393
Pension Benefits [Member] | Derivative [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	555		(372)
Pension Benefits [Member] | Agency securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total			7,793
Level 1 [Member] | Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	341,554		331,486
Level 1 [Member] | Pension Benefits [Member] | Cash and Cash Equivalents [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	5,277		5,183
Level 1 [Member] | Pension Benefits [Member] | Domestic Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	183,538	[1]	169,635	[1]
Level 1 [Member] | Pension Benefits [Member] | International Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	91,546	[1]	76,202	[1]
Level 1 [Member] | Pension Benefits [Member] | US Treasury Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	61,173	[1]	80,426	[1]
Level 1 [Member] | Pension Benefits [Member] | Corporate Bond Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total
Level 1 [Member] | Pension Benefits [Member] | Asset-backed and mortgage-backed securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total
Level 1 [Member] | Pension Benefits [Member] | Municipal Bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total
Level 1 [Member] | Pension Benefits [Member] | Government Bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total
Level 1 [Member] | Pension Benefits [Member] | Commingled funds - equities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total
Level 1 [Member] | Pension Benefits [Member] | Commingled funds - bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total
Level 1 [Member] | Pension Benefits [Member] | Derivative [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	20		40
Level 1 [Member] | Pension Benefits [Member] | Agency securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total
Level 2 [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	71,712		66,968
Level 2 [Member] | Commingled funds - bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	42,989	[2]	40,130	[2]
Level 2 [Member] | Pension Benefits [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	651,677		535,755
Level 2 [Member] | Pension Benefits [Member] | Cash and Cash Equivalents [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	18,410	[3]	23,493	[3]
Level 2 [Member] | Pension Benefits [Member] | Domestic Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total			359	[4]
Level 2 [Member] | Pension Benefits [Member] | International Equity Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	2,609	[4]	2,401	[4]
Level 2 [Member] | Pension Benefits [Member] | US Treasury Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total
Level 2 [Member] | Pension Benefits [Member] | Corporate Bond Securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	248,680	[5]	155,666	[5]
Level 2 [Member] | Pension Benefits [Member] | Asset-backed and mortgage-backed securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	3,848	[5]	2,976	[5]
Level 2 [Member] | Pension Benefits [Member] | Municipal Bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	12,818	[5]	6,334	[5]
Level 2 [Member] | Pension Benefits [Member] | Government Bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	30,521	[5]	17,242	[5]
Level 2 [Member] | Pension Benefits [Member] | Commingled funds - equities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	194,302	[6]	163,510	[6]
Level 2 [Member] | Pension Benefits [Member] | Commingled funds - bonds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	139,954	[7]	156,393	[7]
Level 2 [Member] | Pension Benefits [Member] | Derivative [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total	535		(412)
Level 2 [Member] | Pension Benefits [Member] | Agency securities [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Total			$ 7,793	[5]

[1] Domestic equity securities, international equity securities and U.S. treasuries are valued based on quoted prices in active markets.

[2] The amounts consist of investments in funds not registered with U.S. Securities and Exchange Commission, with underlying investments primarily in the equity securities included in the S&P 500 Index, non-U.S. equity securities and investment grade fixed-income securities. The fair value was determined based on the net asset value per share of each investment at December 31, 2012 and 2011. These funds are classified as Level 2 in the fair value hierarchy as the Company could redeem these investments with the sponsoring investment management organizations at December 31, 2012 and 2011, and with at least monthly frequency on an ongoing basis.

[3] The amounts represent cash equivalents and primarily include short-term investment funds, which consisted of short-term money market instruments that are valued using quoted prices for similar assets and liabilities in active markets.

[4] The amounts include funds that invest primarily in equity securities that are traded less frequently than exchange-traded securities and are valued using inputs that include quoted prices for similar assets in active markets.

[5] The amount consists of investments that are traded less frequently than Level 1 securities and are valued using inputs that include quoted prices for similar assets in active markets and inputs other than quoted prices that are observable for the asset, such as interest rates, yield curves, prepayment speeds, collateral performance, broker/dealer quotes and indices that are observable at commonly quoted intervals.

[6] The amounts consist of investments in funds not registered with U.S. Securities and Exchange Commission, with underlying investments primarily in publicly traded U.S. and non-U.S. equity securities, including securities with small and large market capitalization. The fair value was determined based on the net asset value per share of each investment at December 31, 2012 and 2011. These funds are classified as Level 2 in the fair value hierarchy as the Company could redeem these investments with the sponsoring investment management organizations at December 31, 2012 and 2011, and with at least monthly frequency on an ongoing basis.

[7] The amounts consist of investments in funds not registered with U.S. Securities and Exchange Commission, with underlying investments primarily in Treasury Inflation-Protected Securities and high-yield bonds. The fair value was determined based on the net asset value per share of each investment at December 31, 2012 and 2011. These funds are classified as Level 2 in the fair value hierarchy as the Company could redeem these investments with the sponsoring investment management organizations at December 31, 2012 and 2011, and with at least monthly frequency on an ongoing basis.