Retirement Plans - Additional Information (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Postemployment Benefits [Abstract] | |||
| Expenses related to employee benefit plans | $ 1.0 | $ 1.4 | $ 1.0 |
| Partnership contributions | 4.5 | 4.6 | 3.5 |
| Postretirement expense | $ 0.3 | $ 0.3 | $ 0.3 |