Stock-Based Compensation - Restricted Stock Awards (Details)		12 Months Ended
	Aug. 07, 2018 director shares	Dec. 31, 2018 USD ($) director $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Weighted Average Grant Date Fair Value
Stock based compensation expenses | $		$ 4,387,554	$ 7,174,596
Restricted stock awards
Number of Shares
Outstanding at beginning of period (in shares)		1,380,000	850,000
Granted (in shares)			530,000
Forfeited (in shares)		(333,200)
Outstanding at end of period (in shares)		1,046,800	1,380,000
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share) | $ / shares		$ 7.27	$ 8.23
Granted (in dollars per share) | $ / shares			5.72
Forfeited (in shares) | $ / shares		5.70
Outstanding at end of period (in dollars per share) | $ / shares		$ 7.77	$ 7.27
Vesting period		20 months
Stock based compensation expenses | $		$ 1,300,000	$ 3,300,000
Unrecognized stock-based compensation expenses | $		$ 0
Restricted stock awards - Performance based
Number of Shares
Forfeited (in shares)	(333,200)	(333,200)
Outstanding at end of period (in shares)		146,800
Weighted Average Grant Date Fair Value
Number of former directors | director	2	2
Restricted stock awards - Service based awards
Weighted Average Grant Date Fair Value
Stock based compensation expenses | $		$ 1,292,125	$ 3,316,093
2007 LTIP | Restricted stock awards
Number of Shares
Granted (in shares)			530,000
2007 LTIP | Restricted stock awards - Performance based
Number of Shares
Granted (in shares)			480,000
Weighted Average Grant Date Fair Value
Vesting period			17 months
2007 LTIP | Restricted stock awards - Service based awards
Number of Shares
Granted (in shares)			50,000