Common Stock Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended		13 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Feb. 28, 2019	Dec. 31, 2018	Jun. 13, 2018	Mar. 31, 2018	Feb. 06, 2018	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Common stock, shares authorized (in shares)	100,000,000			100,000,000		100,000,000		100,000,000
Common shares	$ 0.001			$ 0.001		$ 0.001	$ 0.001
Common stock, shares outstanding	29,745,776	29,745,776	30,149,880	29,745,776	30,149,880	29,745,776		29,796,601		30,392,041		31,335,938
Dividends declared (in usd per share)	$ 0.42		$ 0.41	$ 0.97	$ 0.82
Dividends declared	$ 12,800			$ 29,600
Dividends paid			$ (12,700)	$ (25,298)	$ (25,501)
Common shares issued and outstanding upon conversion of all convertible securities (in shares)	30,479,147		30,854,762	30,479,147	30,854,762	30,479,147
Number of shares authorized to be repurchased (in shares)									1,550,000		1,550,000
Shares repurchased (in shares)	0		242,161	50,825	1,186,058	411,915
Average price per share (USD per share)			$ 14.98	$ 15.39	$ 14.83	$ 15.34
Total cost		$ (782)	$ (3,628)	$ (800)	$ (17,593)	$ (6,300)