Statements of Changes in Shareholders' Equity and Redeemable Capital Shares (unaudited) - USD ($) | Total | Retained Earnings [Member] | Redeemable Capital Shares [Member] |
Balance at Dec. 31, 2017 | | | $ 271,881,278 |
Balance, Shares at Dec. 31, 2017 | | | 2,350,000 |
Purchases of Shares | | | $ 453,816,851 |
Purchases of Shares, Shares | | | 3,950,000 |
Redemption of Shares | | | $ (487,918,939) |
Redemption of Shares, Shares | | | (4,250,000) |
Net Increase (Decrease) due to Share Transactions | | | $ (34,102,088) |
Net Increase (Decrease) due to Share Transactions, Shares | | | (300,000) |
Net Comprehensive Income (Loss) | $ (1,849,757) | $ (1,849,757) | |
Adjustment of Redeemable Capital Shares to Redemption Value related to Retained Earnings | 1,849,757 | 1,849,757 | $ (1,849,757) |
Adjustment of Redeemable Capital Shares to Redemption Value | | | (7,907,686) |
Balance at Sep. 30, 2018 | | | $ 228,021,747 |
Balance, Shares at Sep. 30, 2018 | | | 2,050,000 |
Balance at Jun. 30, 2018 | | | $ 268,890,925 |
Balance, Shares at Jun. 30, 2018 | | | 2,400,000 |
Purchases of Shares | | | $ 34,591,809 |
Purchases of Shares, Shares | | | 350,000 |
Redemption of Shares | | | $ (74,747,290) |
Redemption of Shares, Shares | | | (700,000) |
Net Increase (Decrease) due to Share Transactions | | | $ (40,155,481) |
Net Increase (Decrease) due to Share Transactions, Shares | | | (350,000) |
Net Comprehensive Income (Loss) | (500,491) | (500,491) | |
Adjustment of Redeemable Capital Shares to Redemption Value related to Retained Earnings | 500,491 | 500,491 | $ (500,491) |
Adjustment of Redeemable Capital Shares to Redemption Value | | | (213,206) |
Balance at Sep. 30, 2018 | | | $ 228,021,747 |
Balance, Shares at Sep. 30, 2018 | | | 2,050,000 |
Balance at Dec. 31, 2018 | $ 316,828,837 | | $ 316,828,837 |
Balance, Shares at Dec. 31, 2018 | 2,900,000 | | 2,900,000 |
Purchases of Shares | | | $ 197,447,849 |
Purchases of Shares, Shares | | | 1,850,000 |
Redemption of Shares | | | $ (248,252,458) |
Redemption of Shares, Shares | | | (2,300,000) |
Net Increase (Decrease) due to Share Transactions | | | $ (50,804,609) |
Net Increase (Decrease) due to Share Transactions, Shares | | | (450,000) |
Net Comprehensive Income (Loss) | $ (1,435,121) | (1,435,121) | |
Adjustment of Redeemable Capital Shares to Redemption Value related to Retained Earnings | 1,435,121 | 1,435,121 | $ (1,435,121) |
Adjustment of Redeemable Capital Shares to Redemption Value | | | (10,864,366) |
Balance at Sep. 30, 2019 | $ 253,724,741 | | $ 253,724,741 |
Balance, Shares at Sep. 30, 2019 | 2,450,000 | | 2,450,000 |
Balance at Jun. 30, 2019 | | | $ 222,216,366 |
Balance, Shares at Jun. 30, 2019 | | | 2,050,000 |
Purchases of Shares | | | $ 84,609,381 |
Purchases of Shares, Shares | | | 800,000 |
Redemption of Shares | | | $ (42,457,504) |
Redemption of Shares, Shares | | | (400,000) |
Net Increase (Decrease) due to Share Transactions | | | $ 42,151,877 |
Net Increase (Decrease) due to Share Transactions, Shares | | | 400,000 |
Net Comprehensive Income (Loss) | $ (475,453) | (475,453) | |
Adjustment of Redeemable Capital Shares to Redemption Value related to Retained Earnings | 475,453 | $ 475,453 | $ (475,453) |
Adjustment of Redeemable Capital Shares to Redemption Value | | | (10,168,049) |
Balance at Sep. 30, 2019 | $ 253,724,741 | | $ 253,724,741 |
Balance, Shares at Sep. 30, 2019 | 2,450,000 | | 2,450,000 |