Financial Instruments Financial Instruments - Interest Rate Swap Agreements (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative, Number of Instruments Held	3
Derivative, Lower Fixed Interest Rate Range	0.75%
Derivative, Higher Fixed Interest Rate Range	1.64%
Interest Rate Swap [Member]
Derivative [Line Items]
Notional principal amount, interest rate swap agreement(s)	$ 150,000,000	$ 294,900,000
Net receipts (payments) under derivative swap agreements	6,200,000	5,900,000	4,600,000
USD Interest Rate Swap [Member]
Derivative [Line Items]
Notional principal amount, interest rate swap agreement(s)	50,000,000
USD Interest Rate Swap Contract Two and Three [Member]
Derivative [Line Items]
Notional principal amount, interest rate swap agreement(s)	100,000,000
Interest rate swap agreement maturity period	2017
Interest Rate Swap Contract One [Member]
Derivative [Line Items]
Notional principal amount, interest rate swap agreement(s)	50,000,000
Interest rate swap agreement maturity period	2015
Us Term Loan [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Effective interest rate on term loans	2.16%
Accrued Liabilities [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Fair value of liability of total outstanding swap agreements	1,100,000	6,500,000
Other Liabilities [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Fair value of liability of total outstanding swap agreements	$ 100,000	$ 400,000