Fair Value of Financial Instruments - Carrying Value and Fair Value of Long-Term Debt (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	$ 415,438	$ 442,325
Fair Value	429,621	446,025
Fixed-Rate Bonds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	250,000	250,000
Fair Value	264,244	254,533
2.05% Term Loan [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	58,285	58,785
Fair Value	58,224	57,952
Variable Rate Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying Value	107,153	133,540
Fair Value	$ 107,153	$ 133,540