Share-Based Compensation - Restricted common shares and restricted stock units activity (Details)	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Restricted Common Shares
Unvested Shares:
Unvested balance, beginning of year (in shares) | shares	1,619,285
Restricted shares and restricted unit awards granted | shares	384,926
Vested (in shares) | shares	(931,696)
Forfeited (in shares) | shares	(26,594)
Unvested balance, end of year (in shares) | shares	1,045,921
Weighted Average Grant Date Fair Value:
Unvested balance, beginning of year, weighted average grant date fair value | $ / shares	$ 28.88
Weighted average grant date fair value | $ / shares	33.43
Vested, weighted average grant date fair value | $ / shares	28.31
Forfeited, weighted average grant date fair value | $ / shares	30.15
Unvested balance, end of year, weighted average grant date fair value | $ / shares	$ 31.02
Restricted Unit Awards
Unvested Shares:
Unvested balance, beginning of year (in shares) | shares	1,254,558
Restricted shares and restricted unit awards granted | shares	810,815
Vested (in shares) | shares	(422,021)
Forfeited (in shares) | shares	(80,340)
Unvested balance, end of year (in shares) | shares	1,563,012
Weighted Average Grant Date Fair Value:
Unvested balance, beginning of year, weighted average grant date fair value | $ / shares	$ 27.58
Weighted average grant date fair value | $ / shares	32.64
Vested, weighted average grant date fair value | $ / shares	27.75
Forfeited, weighted average grant date fair value | $ / shares	29.36
Unvested balance, end of year, weighted average grant date fair value | $ / shares	$ 30.07