Stockholders' Equity - Restricted Stock Vested by or Granted to Non-Executive Directors (Details) - $ / shares	3 Months Ended												39 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2016
Equity [Abstract]
Price Per Share (usd per share)	$ 17.82	$ 19.17	$ 17.51	$ 18.32	$ 16.46	$ 16.84	$ 19.17	$ 17.36	$ 13.01	$ 15.4	$ 18.17	$ 14.28
Restricted Stock Granted (shares)	6,034	5,605	6,141	5,869	6,242	5,494	4,823	5,328	7,110	6,006	5,093	6,475	70,220