Transfer Between Levels 1, 2 and 3 and Reasons For Those Transfers (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer between Levels 1, 2 and 3	$ 12,205
Reason for Transfer	The interest rate swap and cap instruments were transferred from Level 3 to Level 2 as of March 31, 2012 due to the Corporation's additional analysis of valuation methodologies. These instruments are valued using widely accepted valuation techniques including discounted cash flow analysis using observable inputs such as contractual terms and Libor-based rate curves.
Significant Other Observable Inputs (Level 2) | Interest Rate Swap Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer between Levels 1, 2 and 3	4,862
Significant Other Observable Inputs (Level 2) | Interest Rate Cap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer between Levels 1, 2 and 3	409
Significant Other Observable Inputs (Level 2) | Interest Rate Swap Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer between Levels 1, 2 and 3	6,934
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer between Levels 1, 2 and 3	12,205
Significant Unobservable Inputs (Level 3) | Interest Rate Swap Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer between Levels 1, 2 and 3	4,862
Significant Unobservable Inputs (Level 3) | Interest Rate Cap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer between Levels 1, 2 and 3	409
Significant Unobservable Inputs (Level 3) | Interest Rate Swap Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfer between Levels 1, 2 and 3	$ 6,934