Capital Stock - Issuances of Common Stock (Details) - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Stock Issued During Period Shares New Issues	4,465,555	6,235,017
Stock Issued During Period, Value, New Issues	$ 47,116,000	$ 83,275,000
At the Market Offering Program [Member]
Value of Common Stock Available to be issued under At The Money Program	$ 87,400,000
At the Market Offering Program [Member] | 2015-Q1 [Member]
Share Price	$ 13.66
Stock Issued During Period Shares New Issues	1,210,487
Stock Issued During Period, Value, New Issues	$ 16,175,000
At the Market Offering Program [Member] | 2015-Q2 [Member]
Share Price	$ 13.65
Stock Issued During Period Shares New Issues	5,024,530
Stock Issued During Period, Value, New Issues	$ 67,100,000
At the Market Offering Program [Member] | 2016-Q2 [Member]
Share Price	$ 10.8
Stock Issued During Period Shares New Issues	3,818,802
Stock Issued During Period, Value, New Issues	$ 40,525,000
At the Market Offering Program [Member] | 2016-Q3 [Member]
Stock Issued During Period Shares New Issues	646,753
Stock Issued During Period, Value, New Issues	$ 6,591,000