Summary of Characteristics of Interest Rate Swaps (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivative Instruments:
Weighted average fixed rate	2.48%	2.14%
Forward Starting Pay Fixed Swaps
Derivative Instruments:
Notional amount	$ 800,000
Weighted average fixed rate	3.24%

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant