Subsequent Events (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions			1 Months Ended	3 Months Ended
	Apr. 05, 2016	Apr. 01, 2016	Mar. 31, 2016	Mar. 31, 2016	Mar. 31, 2015
Subsequent Event [Line Items]
Dividend paid to common stockholders				$ 0.32	$ 0.29
Dividends payable, date of record	Mar. 18, 2016			Dec. 17, 2015	Dec. 19, 2014
Dividends payable, date payable				Jan. 06, 2016	Jan. 07, 2015
Subsequent Event [Member]
Subsequent Event [Line Items]
Dividend paid to common stockholders	$ 0.36
Dividends payable, date of record	Mar. 18, 2016
Dividends payable, date payable	Apr. 05, 2016
Common Class A [Member]
Subsequent Event [Line Items]
Shares issued			6,325,000
Net proceeds from issuance of shares			$ 276.0
Common Class A [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Shares issued		6,325,000
Shares issued, price per share		$ 45.50
Common Class A [Member] | Underwriters [Member]
Subsequent Event [Line Items]
Shares issued			825,000
Common Class A [Member] | Underwriters [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Shares issued		825,000