Subsequent Events (Narrative) (Details) - $ / shares				3 Months Ended
	Jul. 16, 2018	Jul. 06, 2018	Jun. 20, 2018	Jun. 30, 2018	Mar. 31, 2018
Subsequent Event [Line Items]
Dividends payable, date of record			Jun. 20, 2018
Common stock
Subsequent Event [Line Items]
Dividends payable, date payable				Apr. 05, 2018	Jan. 05, 2018
Dividend paid to common stockholders				$ 0.41	$ 0.39
Partnership distribution per unit				$ 0.41	$ 0.39
Dividends payable, date of record				Mar. 22, 2018	Dec. 05, 2017
Common stock | Subsequent Event
Subsequent Event [Line Items]
Dividends payable, date payable		Jul. 06, 2018
Dividend paid to common stockholders		$ 0.41
Partnership distribution per unit		$ 0.41
Preferred stock
Subsequent Event [Line Items]
Dividends payable, date payable				Apr. 16, 2018
Dividend paid to common stockholders				$ 0.15
Partnership distribution per unit				$ 0.15
Dividends payable, date of record				Apr. 05, 2018
Preferred stock | Subsequent Event
Subsequent Event [Line Items]
Dividends payable, date payable	Jul. 16, 2018
Dividend paid to common stockholders	$ 0.45
Dividend rate (as a percent)	7.125%