Derivative Financial Instruments - Table of Derivative Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2012
Derivative
Fair value, asset	$ 4,418	$ 0
Fair value, liability	(2,065)	(9,370)
Interest Rate Swap | 3.79%
Derivative
Notional amount		17,304	[1]
Index		LIBOR	[1]
Interest Rate		3.79%	[1]
Fair value, liability		(459)	[1]
Interest Rate Swap | 1.07%
Derivative
Notional amount		75,000	[1]
Index		LIBOR	[1]
Interest Rate		1.07%	[1]
Fair value, liability		(659)	[1]
Interest Rate Swap | 1.23%
Derivative
Notional amount	200,000	200,000
Index	LIBOR	LIBOR
Interest Rate	1.23%	1.23%
Fair value, liability	(1,628)	(5,180)
Interest Rate Swap | 0.86%
Derivative
Notional amount	100,000	100,000
Index	LIBOR	LIBOR
Interest Rate	0.86%	0.86%
Fair value, liability	(437)	(1,310)
Interest Rate Swap | 1.39%
Derivative
Notional amount	50,000	50,000
Index	LIBOR	LIBOR
Interest Rate	1.39%	1.39%
Fair value, asset	1,117
Fair value, liability		(909)
Interest Rate Swap | 1.24%
Derivative
Notional amount	105,000	105,000
Index	LIBOR	LIBOR
Interest Rate	1.24%	1.24%
Fair value, asset	3,301
Fair value, liability		$ (853)

[1] We terminated the interest rate swaps in March 2013.