Earnings Per Share (Details) - USD ($)
$ / shares in Units, $ in Thousands |
3 Months Ended |
12 Months Ended |
Dec. 31, 2016 |
Sep. 30, 2016 |
Jun. 30, 2016 |
Mar. 31, 2016 |
Dec. 31, 2015 |
Sep. 30, 2015 |
Jun. 30, 2015 |
Mar. 31, 2015 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] |
|
|
|
|
|
|
|
|
|
|
|
| Net income |
$ 23,612
|
$ 33,736
|
$ 26,286
|
$ 17,259
|
$ 31,991
|
$ 16,221
|
$ 28,858
|
$ 21,326
|
$ 100,892
|
$ 98,396
|
$ 105,588
|
| Allocation of net income: |
|
|
|
|
|
|
|
|
|
|
|
| Allocation of undistributed income |
|
|
|
|
|
|
|
|
$ 99,619
|
$ 97,123
|
104,315
|
| Denominator: |
|
|
|
|
|
|
|
|
|
|
|
| Antidilutive securities excluded from computation of EPS (shares) |
|
|
|
|
|
|
|
|
17,200
|
21,000
|
|
| Class A [Member] |
|
|
|
|
|
|
|
|
|
|
|
| Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] |
|
|
|
|
|
|
|
|
|
|
|
| Net income |
|
|
|
|
|
|
|
|
$ 98,039
|
$ 95,613
|
102,602
|
| Dividends |
|
|
|
|
|
|
|
|
(1,237)
|
(1,237)
|
(1,237)
|
| Allocation of net income: |
|
|
|
|
|
|
|
|
|
|
|
| Dividends |
|
|
|
|
|
|
|
|
1,237
|
1,237
|
1,237
|
| Allocation of undistributed income |
|
|
|
|
|
|
|
|
$ 96,802
|
$ 94,376
|
$ 101,365
|
| Denominator: |
|
|
|
|
|
|
|
|
|
|
|
| Basic earnings per share - weighted-average shares (in shares) |
|
|
|
|
|
|
|
|
3,436,000
|
3,436,000
|
3,436,000
|
| Effect of dilutive stock options (in shares) |
|
|
|
|
|
|
|
|
1,000
|
1,000
|
1,000
|
| Diluted earnings per share - adjusted weighted-average shares for assumed conversions (in shares) |
|
|
|
|
|
|
|
|
3,437,000
|
3,437,000
|
3,437,000
|
| Basic Earnings Per Share (in dollars per share) |
$ 6.68
|
$ 9.54
|
$ 7.43
|
$ 4.88
|
$ 9.05
|
$ 4.59
|
$ 8.16
|
$ 6.03
|
$ 28.53
|
$ 27.83
|
$ 29.87
|
| Diluted Earnings Per Share (in dollars per share) |
6.67
|
9.54
|
7.43
|
4.88
|
9.04
|
4.59
|
8.16
|
6.03
|
$ 28.53
|
$ 27.82
|
$ 29.85
|
| Common Class B |
|
|
|
|
|
|
|
|
|
|
|
| Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] |
|
|
|
|
|
|
|
|
|
|
|
| Net income |
|
|
|
|
|
|
|
|
$ 2,853
|
$ 2,783
|
$ 2,986
|
| Dividends |
|
|
|
|
|
|
|
|
(36)
|
(36)
|
(36)
|
| Allocation of net income: |
|
|
|
|
|
|
|
|
|
|
|
| Dividends |
|
|
|
|
|
|
|
|
36
|
36
|
36
|
| Allocation of undistributed income |
|
|
|
|
|
|
|
|
$ 2,817
|
$ 2,747
|
$ 2,950
|
| Denominator: |
|
|
|
|
|
|
|
|
|
|
|
| Basic earnings per share - weighted-average shares (in shares) |
|
|
|
|
|
|
|
|
200,000
|
200,000
|
200,000
|
| Effect of dilutive stock options (in shares) |
|
|
|
|
|
|
|
|
0
|
0
|
0
|
| Diluted earnings per share - adjusted weighted-average shares for assumed conversions (in shares) |
|
|
|
|
|
|
|
|
200,000
|
200,000
|
200,000
|
| Basic Earnings Per Share (in dollars per share) |
3.34
|
4.77
|
3.72
|
2.44
|
4.52
|
2.29
|
4.08
|
3.02
|
$ 14.27
|
$ 13.91
|
$ 14.93
|
| Diluted Earnings Per Share (in dollars per share) |
$ 3.34
|
$ 4.77
|
$ 3.72
|
$ 2.44
|
$ 4.52
|
$ 2.29
|
$ 4.08
|
$ 3.02
|
$ 14.27
|
$ 13.91
|
$ 14.93
|