Common Stock - Dividends and Share Repurchase Program (Details) - USD ($)	3 Months Ended						6 Months Ended		12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Aug. 05, 2020
Equity [Abstract]
Dividends per Common Share (in dollars per share)	$ 0.155	$ 0.155	$ 0.14	$ 0.14	$ 0.14	$ 0.14	$ 0.31		$ 0.56
Amount (in thousands)	$ 11,761,000	$ 11,735,000	$ 10,718,000	$ 10,726,000	$ 10,751,000	$ 10,782,000	$ 23,496,000	$ 21,533,000	$ 42,977,000
Dividends Payable [Line Items]
Issued and outstanding common stock authorized to repurchase	100,000,000.0						100,000,000.0
Aggregate purchases of shares in open market before shares will be purchased from Magnus	$ 24,900,000						$ 24,900,000
Shares repurchased (in shares)	0				253,385		243,894	253,385
Amount remaining under current authorizations	$ 63,700,000						$ 63,700,000
Magnus
Dividends Payable [Line Items]
Share repurchase liability	8,800,000		$ 1,800,000				$ 8,800,000		$ 1,800,000
Shares repurchased (in shares)							299,894		56,000
Amount remaining under current authorizations	$ 11,100,000						$ 11,100,000
Subsequent Event
Dividends Payable [Line Items]
Dividends declared and payable (in dollars per share)										$ 0.155