Stockholders' Equity - Common Stock (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Feb. 28, 2017
Stockholders' equity
Proceeds from issuance of common stock		$ 45,125	$ 79,407
Payments of stock issuance costs		784	1,475
Share Repurchase Program
Stockholders' equity
Repurchase Program, number of shares repurchased (in shares)	3,783,936
Repurchase Program, value of shares repurchased	$ 50,100
Repurchase Program, remaining authorized capacity	$ 250,000
Maximum | Share Repurchase Program
Stockholders' equity
Stock Repurchase Program, maximum amount authorized for repurchase				$ 300,000
Common Stock | At The Market
Stockholders' equity
Proceeds from issuance of common stock		45,100	79,400
Payments of stock issuance costs		$ 800	$ 1,500
ATM Program, number of shares sold or issued (in shares)	0	2,590,854	4,876,855
ATM Program, remaining amount authorized for issuance	$ 175,500
Common Stock | Maximum | At The Market
Stockholders' equity
ATM Program, maximum amount authorized for issuance				$ 300,000