Shareholders' Equity - USD ($)	1 Months Ended	3 Months Ended
	Apr. 28, 2017	Mar. 31, 2017	Mar. 31, 2016
Class of Stock [Line Items]
Net proceeds from equity offering		$ 29,959,000	$ 0
Shares issued under dividend reinvestment program		1,114,000
Common Stock [Member]
Class of Stock [Line Items]
Capital shares reserved for future issuances		$ 200,000,000.0
Stock Issued During Period, Shares, New Issues		972,000
Stock Issued During Period, Weighted Average Price		$ 31.31
Net proceeds from equity offering		$ 30,000,000
Shares issued under dividend reinvestment program (in shares)		34,770
Stock issued during period, weighted share price, Dividend Reinstated Plan		$ 32.07
Shares issued under dividend reinvestment program		$ 1,100,000
Subsequent Event [Member] | Common Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	1,100,000
Stock Issued During Period, Weighted Average Price	$ 31.49
Net proceeds from equity offering	$ 34,100,000