Stock-Based Compensation - Summary of Nonvested Stock Awards Granted (Details)	3 Months Ended			6 Months Ended			12 Months Ended
	Jun. 30, 2017 employee shares	Mar. 31, 2017 employee shares	Mar. 31, 2015 executive_officer employee shares	Sep. 30, 2016 employee	Jun. 30, 2016 executive_officer	Dec. 31, 2015 shares	Dec. 31, 2017 $ / shares shares	Dec. 31, 2016 $ / shares shares	Dec. 31, 2015 $ / shares shares
Director group
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of Stock Awards Granted (shares)							51,179		4,273
Vesting Period							1 year		1 year
Weighted Average Grant Date Fair Value (usd per share) | $ / shares							$ 6.35		$ 4.02
Employee group
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of Stock Awards Granted (shares)							641,751	1,250,750	2,493,333
Vesting Period							3 years	2 years	3 years
Weighted Average Grant Date Fair Value (usd per share) | $ / shares							$ 6.31	$ 4.88	$ 3.99
Employee inducement
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of Stock Awards Granted (shares)							100,000	100,000	10,000
Vesting Period							3 years	3 years	3 years
Weighted Average Grant Date Fair Value (usd per share) | $ / shares							$ 6.33	$ 4.94	$ 5.29
Director group (2015)
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of Stock Awards Granted (shares)									17,092
Vesting Period									3 years
Weighted Average Grant Date Fair Value (usd per share) | $ / shares									$ 3.99
Performance-based stock awards (restricted stock units), restricted stock units and restricted stock awards
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of Stock Awards Granted (shares)	183,751						792,930
Weighted Average Grant Date Fair Value (usd per share) | $ / shares							$ 6.32	$ 4.86	$ 4.00
Performance-based stock awards (restricted stock units), restricted stock units and restricted stock awards | Employee group
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of Stock Awards Granted (shares)			1,325,000			1,168,333
Number of employees granted share-based compensation awards | executive_officer			8		5
Performance-based stock awards (restricted stock units), restricted stock units and restricted stock awards | Employee inducement
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of employees granted share-based compensation awards | employee	2		2	3
Performance-based stock awards (restricted stock units), restricted stock units and restricted stock awards | Executive officers
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]
Number of Stock Awards Granted (shares)		458,000
Number of employees granted share-based compensation awards | employee		12