Fair Value Measures and Financial Instruments (Other financial instruments) - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fixed Rate Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	$ 604,328	$ 620,641
Carrying value of debt	591,004	592,459
Variable Rate Debt [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	300,000	304,983
Carrying value of debt	$ 300,000	$ 300,000