Incentive Plan - Summary of Non-Vested Stock Units (Details)	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Number of Shares
Nonvested at beginning of period (in shares) | shares	1,097,010
Granted during period (in shares) | shares	455,650
Vested during period (in shares) | shares	(284,904)
Forfeited during period (in shares) | shares	(54,134)
Nonvested at end of period (in shares) | shares	1,213,622
Weighted Average Grant Date Fair Value Per Share
Nonvested at beginning of period (dollars per share) | $ / shares	$ 36.35
Granted during period (dollars per share) | $ / shares	16.01
Vested during period (dollars per share) | $ / shares	36.21
Forfeited during period (dollars per share) | $ / shares	28.21
Nonvested at end of period (dollars per share) | $ / shares	$ 29.11