Stockholders' Equity, ATM Program and 401(k) Matching Contributions (Details) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 12, 2012	Dec. 14, 2011	Oct. 15, 2013	Feb. 11, 2013
Stockholders' Equity [Line Items]
Issuance of common stock, 401(k) employer match (in shares)	593,198	510,047	316,543
Expense associated with 401(k) plan	$ 1,000,000	$ 1,000,000	$ 800,000
Lazard ATM Program [Member]
Stockholders' Equity [Line Items]
Maximum value of potential common stock available for issue					15,000,000
Percentage sales commission on shares (in hundredths)					3.00%
Issuance of common stock, financing (in shares)				350,374
Issuance of common stock, financing				1,600,000
Net proceeds from issuance of stock				1,500,000
Stifel ATM Program [Member]
Stockholders' Equity [Line Items]
Period of agency agreement							3 years
Maximum value of potential common stock available for issue							25,000,000
Percentage sales commission on shares (in hundredths)							3.00%
Issuance of common stock, financing (in shares)						713,920
Issuance of common stock, financing						2,000,000
Net proceeds from issuance of stock						1,800,000
Amount available under the ATM Program	$ 23,000,000