Subsequent Events (Details) - $ / shares	Jan. 14, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Subsequent Event [Line Items]
Dividends declared, amount per common share		$ 0.15	$ 0.15	$ 0.13	$ 0.13	$ 0.12	$ 0.12	$ 0.08	$ 0.08	$ 0.08	$ 0.08
Subsequent event
Subsequent Event [Line Items]
Dividends declared, amount per common share	$ 0.17
Increase (decrease) in dividends payable, per share	$ 0.02