Share-Based Compensation - Compensation Awards (Details) - 2013 EIP and 2014 NEEIP $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares
Number of Shares Subject To Outstanding Options
Balance at the beginning of period | shares	2,950,472
Granted ( in shares) | shares	600,300
Exercised (in shares) | shares	(68,171)
Forfeited (in shares) | shares	(183,422)
Balance at the end of period | shares	3,299,179
Weighted-Average Exercise Price of Outstanding Options
Balance at the beginning of the period (in dollars per share) | $ / shares	$ 24.75
Granted (in dollars per share) | $ / shares	22.58
Exercised (in dollars per share) | $ / shares	19.96
Forfeited (in dollars per share) | $ / shares	22.49
Balance at the end of the period (in dollars per share) | $ / shares	$ 24.58
Additional disclosures
Aggregate intrinsic value of options outstanding | $	$ 1.2
Aggregate intrinsic value of options exercisable | $	0.8
Total estimated fair value of options vested | $	$ 6.4