Summary of Significant Accounting Policies - Common Stock Repurchase Program and Forms of Outstanding Common Stock (Details)	12 Months Ended
	Dec. 31, 2019 security $ / shares shares	Dec. 31, 2018 $ / shares shares
Common stock
Number of different forms of outstanding common stock | security	2
Common Stock Repurchase Program
Common Stock Repurchase Program
Repurchase of shares of common stock (in shares) | shares	59,700	303,500
Average cost of shares repurchased (in dollars per share) | $ / shares	$ 26.74	$ 30.36