Stockholders' Equity (Stock Transactions - Narrative) (Details) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Apr. 30, 2016 USD ($) $ / shares shares	Mar. 31, 2016 USD ($) investment_bank $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Apr. 29, 2016 shares	Feb. 19, 2016 shares	Feb. 17, 2016 investment_bank
Class of Stock [Line Items]
Net proceeds from issuance of common stock | $		$ 70,181	$ 31,910
Dividends per share declared to common stockholders (in dollars per share)		$ 0.30	$ 0.30
At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Number of investment banks in sales agreements | investment_bank		5
Shares authorized to be sold under the program | shares					10,000,000
Issuance of common stock (shares) | shares		2,416,837
Net proceeds from issuance of common stock | $		$ 69,700
Previous At the Market Equity Offering Program [Member]
Class of Stock [Line Items]
Number of investment banks in sales agreements | investment_bank						1
Issuance of common stock (shares) | shares			664,298
Subsequent Event [Member] | At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Issuance of common stock (shares) | shares	564,410
Net proceeds from issuance of common stock | $	$ 17,000
Number of authorized shares remaining under offering program | shares				7,683,051
Minimum [Member] | At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Issuance of common stock (price per share)		$ 28.31
Minimum [Member] | Subsequent Event [Member] | At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Issuance of common stock (price per share)	$ 30.11
Maximum [Member] | At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Issuance of common stock (price per share)		30.16
Maximum [Member] | Subsequent Event [Member] | At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Issuance of common stock (price per share)	30.82
Weighted Average [Member] | At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Issuance of common stock (price per share)		$ 29.29
Weighted Average [Member] | Subsequent Event [Member] | At The Market Equity Offering Program [Member]
Class of Stock [Line Items]
Issuance of common stock (price per share)	$ 30.57