Common Stock and Dividends (Details) - USD ($)					1 Months Ended	6 Months Ended
	Aug. 02, 2017	Apr. 17, 2017	Apr. 18, 2016	Apr. 09, 2016	Apr. 30, 2009	Jun. 30, 2017	Apr. 03, 2017
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
Maximum cash dividend paid in semi-annual period (in dollars per share)						$ 0.33
Cash dividends paid to common shareholders (in dollars per share)		$ 0.33	$ 0.29
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	9,243,999
Cumulative cost of shares repurchased under all stock repurchase programs	$ 271,224,000