Stockholders' Equity - Shares Repurchased (Details) - Eleventh Plan - $ / shares |
3 Months Ended | 6 Months Ended | 42 Months Ended | ||
|---|---|---|---|---|---|
Jun. 30, 2016 |
Jun. 30, 2015 |
Jun. 30, 2016 |
Jun. 30, 2015 |
Jun. 30, 2016 |
|
| Equity, Class of Treasury Stock [Line Items] | |||||
| Repurchased shares | 0 | 304,600 | 100,000 | 441,966 | 541,966 |
| Stock repurchase average share price (in usd per share) | $ 0.00 | $ 16.88 | $ 17.05 | $ 16.64 | $ 16.72 |