Derivatives and Hedging (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Interest Rate Derivatives
Notional value	$ 2,134,751,000		$ 2,134,751,000		$ 2,186,251,000
Unrealized gains (losses) included in accumulated other comprehensive loss	33,600,000		33,600,000		8,800,000
Amount of hedge ineffectiveness	0	$ 0	0	$ 0
Net unrealized gains in accumulated other comprehensive income expected to be reclassified into interest expense within the next 12 months	8,000,000		8,000,000
Interest Rate Cash Flow Hedge Derivative at Fair Value, Net	33,639,000		33,639,000		8,846,000
Designated as Hedging Instrument | Swap-cash flow, hedge type two
Derivatives and Hedging
Interest rate swap asset	0		0
Interest rate swap liability					(38,000)
Interest Rate Derivatives
Notional value	$ 0		$ 0		175,000,000
Interest rate	1.5625%		1.5625%
Designated as Hedging Instrument | Swap-cash flow, hedge type three
Derivatives and Hedging
Interest rate swap asset	$ 0		$ 0
Interest rate swap liability					(71,000)
Interest Rate Derivatives
Notional value	$ 0		$ 0		175,000,000
Interest rate	1.635%		1.635%
Designated as Hedging Instrument | Swap-cash flow, hedge type four
Derivatives and Hedging
Interest rate swap asset	$ 10,000		$ 10,000
Interest rate swap liability					(23,000)
Interest Rate Derivatives
Notional value	$ 15,593,000		$ 15,593,000		15,758,000
Interest rate	1.825%		1.825%
Designated as Hedging Instrument | Swap-cash flow, hedge type five
Derivatives and Hedging
Interest rate swap asset	$ 15,000		$ 15,000
Interest rate swap liability					(14,000)
Interest Rate Derivatives
Notional value	$ 15,593,000		$ 15,593,000		15,758,000
Interest rate	1.751%		1.751%
Designated as Hedging Instrument | Swap-cash flow, hedge type six
Derivatives and Hedging
Interest rate swap asset	$ 28,000		$ 28,000
Interest rate swap liability					(57,000)
Interest Rate Derivatives
Notional value	$ 38,273,000		$ 38,273,000		38,678,000
Interest rate	1.825%		1.825%
Designated as Hedging Instrument | Swap-cash flow, hedge type seven
Derivatives and Hedging
Interest rate swap asset	$ 38,000		$ 38,000
Interest rate swap liability					(35,000)
Interest Rate Derivatives
Notional value	$ 39,217,000		$ 39,217,000		39,632,000
Interest rate	1.751%		1.751%
Designated as Hedging Instrument | Swap-cash flow, hedge type eight
Derivatives and Hedging
Interest rate swap asset	$ 13,000		$ 13,000
Interest rate swap liability					(25,000)
Interest Rate Derivatives
Notional value	$ 17,010,000		$ 17,010,000		17,190,000
Interest rate	1.825%		1.825%
Designated as Hedging Instrument | Swap-cash flow, hedge type nine
Derivatives and Hedging
Interest rate swap asset	$ 15,000		$ 15,000
Interest rate swap liability					(14,000)
Interest Rate Derivatives
Notional value	$ 16,065,000		$ 16,065,000		16,235,000
Interest rate	1.751%		1.751%
Designated as Hedging Instrument | Swap-cash flow, hedge type ten
Derivatives and Hedging
Interest rate swap asset	$ 232,000		$ 232,000
Interest rate swap liability					(383,000)
Interest Rate Derivatives
Notional value	$ 125,000,000		$ 125,000,000		125,000,000
Interest rate	2.018%		2.018%
Designated as Hedging Instrument | Swap-cash flow, hedge type eleven
Derivatives and Hedging
Interest rate swap asset	$ 242,000		$ 242,000
Interest rate swap liability					(213,000)
Interest Rate Derivatives
Notional value	$ 100,000,000		$ 100,000,000		100,000,000
Interest rate	1.944%		1.944%
Designated as Hedging Instrument | Swap-cash flow, hedge type twelve
Derivatives and Hedging
Interest rate swap asset	$ 1,009,000		$ 1,009,000		836,000
Interest Rate Derivatives
Notional value	$ 125,000,000		$ 125,000,000		125,000,000
Interest rate	1.2715%		1.2715%
Designated as Hedging Instrument | Swap-cash flow, hedge type thirteen
Derivatives and Hedging
Interest rate swap asset	$ 251,000		$ 251,000
Interest rate swap liability					(230,000)
Interest Rate Derivatives
Notional value	$ 100,000,000		$ 100,000,000		100,000,000
Interest rate	1.9615%		1.9615%
Designated as Hedging Instrument | Swap-cash flow, hedge type fourteen
Derivatives and Hedging
Interest rate swap asset	$ 171,000		$ 171,000
Interest rate swap liability					(43,000)
Interest Rate Derivatives
Notional value	$ 50,000,000		$ 50,000,000		50,000,000
Interest rate	1.85%		1.85%
Designated as Hedging Instrument | Swap-cash flow, hedge type fifteen
Derivatives and Hedging
Interest rate swap asset	$ 186,000		$ 186,000
Interest rate swap liability					(19,000)
Interest Rate Derivatives
Notional value	$ 50,000,000		$ 50,000,000		50,000,000
Interest rate	1.8115%		1.8115%
Designated as Hedging Instrument | Swap-cash flow, hedge type sixteen
Derivatives and Hedging
Interest rate swap asset	$ 107,000		$ 107,000		13,000
Interest Rate Derivatives
Notional value	$ 25,000,000		$ 25,000,000		25,000,000
Interest rate	1.7445%		1.7445%
Designated as Hedging Instrument | Swap-cash flow, hedge type seventeen
Derivatives and Hedging
Interest rate swap asset	$ 517,000		$ 517,000		202,000
Interest Rate Derivatives
Notional value	$ 33,000,000		$ 33,000,000		33,000,000
Interest rate	1.80%		1.80%
Designated as Hedging Instrument | Swap-cash flow, hedge type eighteen
Derivatives and Hedging
Interest rate swap asset	$ 1,284,000		$ 1,284,000		502,000
Interest Rate Derivatives
Notional value	$ 82,000,000		$ 82,000,000		82,000,000
Interest rate	1.80%		1.80%
Designated as Hedging Instrument | Swap-cash flow, hedge type nineteen
Derivatives and Hedging
Interest rate swap asset	$ 548,000		$ 548,000		214,000
Interest Rate Derivatives
Notional value	$ 35,000,000		$ 35,000,000		35,000,000
Interest rate	1.80%		1.80%
Designated as Hedging Instrument | Swap-cash flow, hedge type twenty
Derivatives and Hedging
Interest rate swap asset	$ 2,684,000		$ 2,684,000		803,000
Interest Rate Derivatives
Notional value	$ 143,000,000		$ 143,000,000		143,000,000
Interest rate	1.80816%		1.80816%
Designated as Hedging Instrument | Swap-cash flow, hedge type twenty one
Derivatives and Hedging
Interest rate swap asset	$ 1,570,000		$ 1,570,000		769,000
Interest Rate Derivatives
Notional value	$ 50,000,000		$ 50,000,000		50,000,000
Interest rate	1.6125%		1.6125%
Designated as Hedging Instrument | Swap-cash flow, hedge type twenty two
Derivatives and Hedging
Interest rate swap asset	$ 1,656,000		$ 1,656,000		869,000
Interest Rate Derivatives
Notional value	$ 50,000,000		$ 50,000,000		50,000,000
Interest rate	1.5555%		1.5555%
Designated as Hedging Instrument | Swap-cash flow, hedge type twenty three
Derivatives and Hedging
Interest rate swap asset	$ 1,424,000		$ 1,424,000		598,000
Interest Rate Derivatives
Notional value	$ 50,000,000		$ 50,000,000		50,000,000
Interest rate	1.7095%		1.7095%
Designated as Hedging Instrument | Swap-cash flow, hedge type twenty four
Derivatives and Hedging
Interest rate swap asset	$ 4,235,000		$ 4,235,000		2,880,000
Interest Rate Derivatives
Notional value	$ 100,000,000		$ 100,000,000		100,000,000
Interest rate	1.15%		1.15%
Designated as Hedging Instrument | Swap-cash flow, hedge type twenty five
Derivatives and Hedging
Interest rate swap asset	$ 4,094,000		$ 4,094,000		2,726,000
Interest Rate Derivatives
Notional value	$ 100,000,000		$ 100,000,000		100,000,000
Interest rate	1.20%		1.20%
Designated as Hedging Instrument | Swap-cash flow, hedge type twenty six
Derivatives and Hedging
Interest rate swap asset	$ 1,048,000		$ 1,048,000
Interest rate swap liability					(144,000)
Interest Rate Derivatives
Notional value	$ 75,000,000		$ 75,000,000		75,000,000
Interest rate	2.15%		2.15%
Designated as Hedging Instrument | Swap-cash flow, hedge type twenty seven
Derivatives and Hedging
Interest rate swap asset	$ 1,565,000		$ 1,565,000		415,000
Interest Rate Derivatives
Notional value	$ 75,000,000		$ 75,000,000		75,000,000
Interest rate	1.91%		1.91%
Designated as Hedging Instrument | Interest Rate, Swap Hedge, Type Twenty Eight [Member]
Derivatives and Hedging
Interest rate swap asset	$ 3,735,000		$ 3,735,000
Interest rate swap liability					(413,000)
Interest Rate Derivatives
Notional value	$ 200,000,000		$ 200,000,000		200,000,000
Interest rate	2.29%		2.29%
Designated as Hedging Instrument | Interest Rate, Swap Hedge, Type Twenty Nine [Member]
Derivatives and Hedging
Interest rate swap asset	$ 2,354,000		$ 2,354,000
Interest rate swap liability					(259,000)
Interest Rate Derivatives
Notional value	$ 125,000,000		$ 125,000,000		125,000,000
Interest rate	2.29%		2.29%
Designated as Hedging Instrument | Interest Rate, Swap Hedge, Type Thirty [Member]
Derivatives and Hedging
Interest rate swap asset	$ 3,066,000		$ 3,066,000		0
Interest Rate Derivatives
Notional value	$ 200,000,000		$ 200,000,000		0
Interest rate	2.38%		2.38%
Designated as Hedging Instrument | Interest Rate, Swap Hedge, Type Thirty One [Member]
Derivatives and Hedging
Interest rate swap asset	$ 1,542,000		$ 1,542,000		0
Interest Rate Derivatives
Notional value	$ 100,000,000		$ 100,000,000		0
Interest rate	2.38%		2.38%
Interest Expense
Interest Rate Derivatives
Amount reclassified from accumulated other comprehensive income into interest expense	$ 700,000	$ (2,000,000)	$ 300,000	$ (4,900,000)
Accounts payable and other liabilities | Interest rate swap
Derivatives and Hedging
Interest rate swap liability					(2,000,000)
Prepaid expenses and other assets | Interest rate swap
Derivatives and Hedging
Interest rate swap asset	$ 33,600,000		$ 33,600,000		$ 10,800,000