Stockholders' Equity - Capital Structure (Details) $ / shares in Units, $ in Millions	1 Months Ended		6 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares	May 31, 2019 USD ($)	Jun. 30, 2020 USD ($) Vote / shares shares	Dec. 16, 2016 USD ($)
Subsidiary, Sale of Stock [Line Items]
Common stock sales agreement, authorized amount	$ 80.0	$ 50.0
Common stock sales agreement, gross sales			$ 12.4
Common stock sales agreement, net sales			$ 12.1
Common stock sales agreement, commission percentage	3.00%	3.00%
Shares issued | shares			141,678
Common stock, voting right per share | Vote / shares			1
Underwritten Public Offering
Subsidiary, Sale of Stock [Line Items]
Shares issued | shares	2,300,000
Share Price | $ / shares	$ 87.00
Proceeds from issuance of common stock, gross	$ 200.1
Proceeds from issuance of common stock, net	$ 187.1
2016 Shelf Registration
Subsidiary, Sale of Stock [Line Items]
Shelf Registration Statement, maximum aggregate amount issuable				$ 150.0
2019 Shelf Registration
Subsidiary, Sale of Stock [Line Items]
Proceeds from issuance of common stock, gross			$ 219.8