Common Stock and Dividends (Details) - USD ($)							1 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Nov. 05, 2018	Oct. 16, 2018	Apr. 16, 2018	Oct. 16, 2017	Apr. 17, 2017	Apr. 09, 2017	Apr. 30, 2009	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2008	Apr. 03, 2018
Common Stock and Dividends
Warrants to purchase entity's common stock (in shares)											1,326,238
Warrants, exercise price (in dollars per share)											$ 24.43
Warrants, term											10 years
Payments for Repurchase of Warrants								$ 29,005,000		$ 29,005,000
Maximum cash dividend paid in semi-annual period (in dollars per share)									$ 0.33
Cash dividends paid to common shareholders (in dollars per share)		$ 0.42	$ 0.33	$ 0.33	$ 0.33
Repurchase of common stock, authorized amount							$ 40,000,000					$ 40,000,000
Period of repurchase of common stock						12 months	12 months
Cumulative number of shares repurchased under all stock repurchase programs	9,246,956
Cumulative cost of shares repurchased under all stock repurchase programs	$ 271,347,000