Summary of Significant Accounting Policies - Share Repurchase Program (Details) - USD ($) |
12 Months Ended | |||
|---|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Feb. 28, 2017 |
Apr. 30, 2016 |
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Treasury stock, shares, acquired | 574,848 | 1,298,418 | ||
| Treasury stock, value, acquired | $ 3,412,000 | $ 6,387,000 | ||
| Repurchase fees | $ 23,000 | $ 52,000 | ||
| Treasury Stock | ||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Treasury stock, shares, acquired | (574,848) | (1,298,418) | ||
| Treasury stock, value, acquired | $ 3,412,000 | $ 6,387,000 | ||
| Class A Common Stock | ||||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||||
| Stock repurchase program, authorized amount (up to) | $ 15,000,000 | $ 10,000,000 | ||
| X | ||||||||||
- Definition Stock Repurchase Program, Repurchase Fees No definition available.
|
| X | ||||||||||
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available.
|
| X | ||||||||||
- Definition Amount of stock repurchase plan authorized. No definition available.
|
| X | ||||||||||
- Definition Number of shares that have been repurchased during the period and are being held in treasury. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Definition Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method. Reference 1: http://www.xbrl.org/2003/role/presentationRef
|
| X | ||||||||||
- Details
|
| X | ||||||||||
- Details
|