Common Stock Capitalization (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands |
3 Months Ended | 9 Months Ended | 16 Months Ended | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Jul. 26, 2019 |
Jul. 23, 2019 |
Sep. 30, 2019 |
Mar. 31, 2019 |
Sep. 30, 2018 |
Sep. 30, 2019 |
Sep. 30, 2018 |
Sep. 30, 2019 |
Jul. 22, 2019 |
Jun. 30, 2019 |
Feb. 28, 2019 |
Dec. 31, 2018 |
Jun. 30, 2018 |
Jun. 13, 2018 |
Feb. 06, 2018 |
Dec. 31, 2017 |
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| 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 | 33,774,386 | 30,155,055 | 33,774,386 | 30,155,055 | 33,774,386 | 29,745,776 | 29,796,601 | 30,149,880 | 31,335,938 | ||||||||||
| Dividends declared (in usd per share) | $ 0.42 | $ 0.41 | $ 1.39 | $ 1.23 | |||||||||||||||
| Dividends declared | $ 14,500 | $ 44,100 | |||||||||||||||||
| Dividends paid | $ (12,700) | $ (39,226) | $ (38,152) | ||||||||||||||||
| Common shares issued and outstanding upon conversion of all convertible securities (in shares) | 34,518,699 | 30,871,043 | 34,518,699 | 30,871,043 | 34,518,699 | ||||||||||||||
| Number of shares authorized to be repurchased (in shares) | 1,550,000 | 1,550,000 | |||||||||||||||||
| Shares repurchased (in shares) | 0 | 0 | 50,825 | 1,186,058 | 411,915 | ||||||||||||||
| Average price per share (USD per share) | $ 15.39 | $ 14.83 | $ 15.34 | ||||||||||||||||
| Total cost | $ (782) | $ 0 | $ (800) | $ (17,593) | $ (6,300) | ||||||||||||||
| Stock Issued During Period, Shares, New Issues | 525,000 | 3,500,000 | 4,025,000 | [1] | 4,025,000 | ||||||||||||||
| Proceeds from issuance of shares, net | $ 9,100 | $ 60,700 | |||||||||||||||||
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