Subsequent Event (Detail) - USD ($) $ in Millions		3 Months Ended
	May 05, 2021	Mar. 31, 2021	Mar. 31, 2020
Subsequent Event [Line Items]
Number of shares sold by the entity		550,803	39,607
At The Market Issuance Sales Agreement [Member]
Subsequent Event [Line Items]
Number of shares sold by the entity		590,410
Value of shares sold by the entity		$ 72.8
Net proceeds after deducting commissions and other transactions costs		71.0
Remaining reserved amount under shelf registration		$ 127.2
Subsequent Event [Member] | At The Market Issuance Sales Agreement [Member]
Subsequent Event [Line Items]
Number of shares sold by the entity	521,426
Value of shares sold by the entity	$ 62.6
Net proceeds after deducting commissions and other transactions costs	61.9
Remaining reserved amount under shelf registration	$ 64.6