Equity Incentive Compensation Plans and Other Long-term Incentive Programs - Non-Cash Stock-Based Compensation Cost Related to Equity Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock Based Compensation [Line Items]
Non-cash stock-based compensation equity awards	$ 2,296	$ 2,248	$ 5,018	$ 3,675
Nonvested Equity Shares [Member]
Stock Based Compensation [Line Items]
Non-cash stock-based compensation equity awards	1,533	1,520	3,329	2,850
Nonvested Equity Common Stock Units
Stock Based Compensation [Line Items]
Non-cash stock-based compensation equity awards	318	277	612	447
Nonvested Performance Cash Units
Stock Based Compensation [Line Items]
Cash Unit Based Compensation Awards	$ 445	$ 451	$ 1,077	$ 378