Derivatives and Hedging (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012
Financial Instruments: Derivatives and Hedging
Notional value	$ 1,071,000,000			$ 1,071,000,000			$ 131,000,000
Total	(11,484,000)			(11,484,000)			(470,000)
Unrealized gains included in accumulated other comprehensive loss	11,400,000			11,400,000			0
Amount of ineffective hedges	0		0	0		0
Interest rate swap
Financial Instruments: Derivatives and Hedging
Fair value assets	2,765,000			2,765,000
Fair value liabilities	(14,200,000)			(14,200,000)			(500,000)
Not Designated as Hedging Instrument | Swap-cash flow, hedge type one
Financial Instruments: Derivatives and Hedging
Notional value	40,000,000	[1]		40,000,000	[1]		40,000,000	[1]
Hedge interest rate (as a percent)	1.00%	[1]		1.00%	[1]
Fair value liabilities	(31,000)	[1]		(31,000)	[1]		(265,000)	[1]
Not Designated as Hedging Instrument | Swap-cash flow, hedge type two
Financial Instruments: Derivatives and Hedging
Notional value	31,000,000	[1]		31,000,000	[1]		31,000,000	[1]
Hedge interest rate (as a percent)	1.00%	[1]		1.00%	[1]
Fair value liabilities	(24,000)	[1]		(24,000)	[1]		(205,000)	[1]
Not Designated as Hedging Instrument | Interest rate cap, hedge type one
Financial Instruments: Derivatives and Hedging
Notional value	0	[1]		0	[1]		60,000,000	[1]
Hedge interest rate (as a percent)	1.00%	[1]		1.00%	[1]
Fair value liabilities	0	[1]		0	[1]		0	[1]
Designated as Hedging Instrument | Swap-cash flow, hedge type one
Financial Instruments: Derivatives and Hedging
Notional value	275,000,000	[2]		275,000,000	[2]		0	[2]
Hedge interest rate (as a percent)	1.1175%	[2]		1.1175%	[2]
Fair value assets	2,765,000	[2]		2,765,000	[2]
Fair value liabilities							0	[2]
Designated as Hedging Instrument | Swap-cash flow, hedge type two
Financial Instruments: Derivatives and Hedging
Notional value	175,000,000	[2]		175,000,000	[2]		0	[2]
Hedge interest rate (as a percent)	1.5625%	[2]		1.5625%	[2]
Fair value liabilities	(2,792,000)	[2]		(2,792,000)	[2]		0	[2]
Designated as Hedging Instrument | Swap-cash flow, hedge type three
Financial Instruments: Derivatives and Hedging
Notional value	175,000,000	[2]		175,000,000	[2]		0	[2]
Hedge interest rate (as a percent)	1.635%	[2]		1.635%	[2]
Fair value liabilities	(3,362,000)	[2]		(3,362,000)	[2]		0	[2]
Designated as Hedging Instrument | ISwap-cash flow, hedge type four
Financial Instruments: Derivatives and Hedging
Notional value	16,500,000	[2]		16,500,000	[2]		0	[2]
Hedge interest rate (as a percent)	1.825%	[2]		1.825%	[2]
Fair value liabilities	(354,000)	[2]		(354,000)	[2]		0	[2]
Designated as Hedging Instrument | Swap-cash flow, hedge type five
Financial Instruments: Derivatives and Hedging
Notional value	16,500,000	[2]		16,500,000	[2]		0	[2]
Hedge interest rate (as a percent)	1.751%	[2]		1.751%	[2]
Fair value liabilities	(294,000)	[2]		(294,000)	[2]		0	[2]
Designated as Hedging Instrument | Swap-cash flow, hedge type six
Financial Instruments: Derivatives and Hedging
Notional value	40,500,000	[2]		40,500,000	[2]		0	[2]
Hedge interest rate (as a percent)	1.825%	[2]		1.825%	[2]
Fair value liabilities	(869,000)	[2]		(869,000)	[2]		0	[2]
Designated as Hedging Instrument | Swap-cash flow, hedge type seven
Financial Instruments: Derivatives and Hedging
Notional value	41,500,000	[2]		41,500,000	[2]		0	[2]
Hedge interest rate (as a percent)	1.751%	[2]		1.751%	[2]
Fair value liabilities	(740,000)	[2]		(740,000)	[2]		0	[2]
Designated as Hedging Instrument | Swap-cash flow, hedge type eight
Financial Instruments: Derivatives and Hedging
Notional value	18,000,000	[2]		18,000,000	[2]		0	[2]
Hedge interest rate (as a percent)	1.825%	[2]		1.825%	[2]
Fair value liabilities	(386,000)	[2]		(386,000)	[2]		0	[2]
Designated as Hedging Instrument | Swap-cash flow, hedge type nine
Financial Instruments: Derivatives and Hedging
Notional value	17,000,000	[2]		17,000,000	[2]		0	[2]
Hedge interest rate (as a percent)	1.751%	[2]		1.751%	[2]
Fair value liabilities	(303,000)	[2]		(303,000)	[2]		0	[2]
Designated as Hedging Instrument | Swap-cash flow, hedge type ten
Financial Instruments: Derivatives and Hedging
Notional value	125,000,000	[2]		125,000,000	[2]		0	[2]
Hedge interest rate (as a percent)	2.018%	[2]		2.018%	[2]
Fair value liabilities	(3,054,000)	[2]		(3,054,000)	[2]		0	[2]
Designated as Hedging Instrument | Swap-cash flow, hedge type eleven
Financial Instruments: Derivatives and Hedging
Notional value	100,000,000	[2]		100,000,000	[2]		0	[2]
Hedge interest rate (as a percent)	1.944%	[2]		1.944%	[2]
Fair value liabilities	$ (2,040,000)	[2]		$ (2,040,000)	[2]		$ 0	[2]

[1] Not designated as a cash flow hedge

[2] Designated as a cash flow hedge