Fair Value of Financial Instruments - Carrying Value and Fair Value Measurements of Financial Assets and Liabilities on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Assets
Available for sale securities	$ 277,719	$ 405,355
Derivative instruments	1,200
Liabilities
Derivative instruments		6,900
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Available for sale securities	0
Liabilities
Derivative instruments	0
Significant Other Observable Inputs (Level 2) [Member]
Assets
Available for sale securities	277,719	405,355
Liabilities
Derivative instruments	4,317	6,854
Significant Unobservable Inputs (Level 3) [Member]
Assets
Available for sale securities	0
Total	12,172	26,747
Liabilities
Derivative instruments	0
Fair Value, Measurements, Recurring [Member]
Assets
Available for sale securities	277,719	405,355
Derivative instruments	1,157
Total	278,876
Liabilities
Derivative instruments	4,317	6,854
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Available for sale securities	0
Derivative instruments	0
Total	0
Liabilities
Derivative instruments	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets
Available for sale securities	277,719	405,355
Derivative instruments	1,157
Total	278,876
Liabilities
Derivative instruments	4,317	6,854
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets
Available for sale securities	0
Derivative instruments	0
Total	0
Liabilities
Derivative instruments	$ 0