Summary of Significant Accounting Policies - Components of rental income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Property operating income	$ 336,409	$ 306,550	$ 285,304
Single-tenant net lease	63,871	67,238	65,252
Straight-line rent	7,201	9,545	10,969
Rental income	$ 407,481	$ 383,333	$ 361,525