Stockholders' Equity - Common Stock (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($) shares	Jun. 30, 2019 USD ($) shares
Shares Issued
Dividend reinvestment plan issuances (in shares) | shares	264,153	4,304,712
Option exercises (in shares) | shares	251	10,736
Equity shelf program issuances (in shares) | shares	6,799,978	4,384,045
Preferred stock conversions (in shares) | shares		12,712,452
Stock incentive plans, net of forfeitures (in shares) | shares	183,398	167,565
Totals (in shares) | shares	7,247,780	21,579,510
Average Price
Dividend reinvestment plan issuances (in dollars per share)	72.33	75.20
Option exercises (in dollars per share)	47.81	51.32
Equity shelf plan issuances (in dollars per share)	86.48	74.97
Gross Proceeds
Dividend reinvestment plan issuances	$ 19,105	$ 323,724
Option exercises	12	551
Equity shelf plan issuances	588,072	328,665
Totals	607,189	652,940
Net Proceeds
Dividend reinvestment plan issuances	19,105	320,243
Option exercises	12	551
Equity shelf plan issuances	576,196	326,362
Totals	$ 595,313	$ 647,156