Stockholders' Equity - Common Stock (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($) shares
Shares Issued
Dividend reinvestment plan issuances (in shares) | shares	264,153	4,438,787
Option exercises (in shares) | shares	251	10,736
Equity shelf program issuances (in shares) | shares	6,799,978	4,729,045
Preferred stock conversions (in shares) | shares		12,712,452
Stock incentive plans, net of forfeitures (in shares) | shares	185,994	192,237
Totals (in shares) | shares	7,250,376	22,083,257
Average Price
Dividend reinvestment plan issuances (in dollars per share)	72.33	75.59
Option exercises (in dollars per share)	47.81	51.32
Equity shelf plan issuances (in dollars per share)	86.48	75.24
Gross Proceeds
Dividend reinvestment plan issuances	$ 19,105	$ 335,535
Option exercises	12	551
Equity shelf plan issuances	588,072	355,803
Totals	607,189	691,889
Net Proceeds
Dividend reinvestment plan issuances	19,105	332,054
Option exercises	12	551
Equity shelf plan issuances	576,196	353,500
Totals	$ 595,313	$ 686,105