Share-Based Compensation - Nonvested Restricted Stock (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) Installment $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Nonvested Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Common shares reserved for stock option and restricted stock grants	8,600,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting rate, initial year	33.33%
Quarterly award vesting installments after initial year | Installment	8
Nonvested Awards, Number of Shares [Roll Forward]
Nonvested awards, beginning balance (in shares)	107,954	40,416	107,095
Granted (in shares)	388,089	91,658	5,623
Vested (in shares)	(68,504)	(24,120)	(68,788)
Forfeited (in shares)	0	0	(3,514)
Nonvested awards, ending balance (in shares)	427,539	107,954	40,416
Nonvested Awards, Weighted Average Grant Date Fair Value [Roll Forward]
Nonvested awards outstanding, beginning balance (in dollars per share) | $ / shares	$ 52.08	$ 58.60	$ 45.74
Granted (in dollars per share) | $ / shares	24.37	50.54	76.47
Vested (in dollars per share) | $ / shares	52.49	57.14	40.67
Forfeited (in dollars per share) | $ / shares	0	0	46.24
Nonvested awards outstanding, ending balance (in dollars per share) | $ / shares	$ 26.86	$ 52.08	$ 58.60
Stock compensation expense recognized on restricted grants | $	$ 4.3	$ 2.9	$ 2.4
Unrecognized compensation cost, share-based compensation arrangements | $	$ 9.1
Weighted average period to recognize nonvested awards (in years)	2 years 9 months
Fair value of shares vested during period | $	$ 3.6	$ 1.4	$ 2.8