Condensed Consolidated Statements of Stockholders' Equity (unaudited) - 9 months ended Sep. 30, 2018 - USD ($) $ in Thousands	Total	Class A Common Stock	Class B Common Stock	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Total Stockholders' Equity	Non-controlling Interests	Private Perpetual Preferred Units
Beginning balance (in shares) at Dec. 31, 2017		160,424,575	1,052,469	160,425,000	1,052,000
Beginning balance at Dec. 31, 2017	$ 1,977,737			$ 1,604	$ 11	$ 1,128,460	$ (8,555)	$ 46,762	$ 1,168,282	$ 801,451	$ 8,004
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Class A shares (shares)				284,000
Issuance of Class A shares	4,749			$ 3		4,746			4,749
Conversion of operating partnership units and Class B shares to Class A shares (in shares)				7,444,000	(8,000)
Conversion of operating partnership units and Class B shares to Class A shares	0			$ 74	$ (1)	31,605	(18)		31,660	(31,660)
Equity compensation:
LTIP units	13,795									13,795
Restricted stock, net of forfeitures (in shares)				24,000
Restricted stock, net of forfeitures	269					269			269
Dividends and distributions	(95,960)							(52,519)	(52,519)	(42,739)	(702)
Net income	77,472							42,761	42,761	34,009	702
Other comprehensive income (loss)	11,389						6,344		6,344	5,045
Ending balance (in shares) at Sep. 30, 2018		168,178,734	1,044,169	168,177,000	1,044,000
Ending balance at Sep. 30, 2018	$ 1,989,451			$ 1,681	$ 10	$ 1,165,080	$ (2,229)	$ 37,004	$ 1,201,546	$ 779,901	$ 8,004