Benefit Plans - Summary of Company's Restricted Stock Units Activity (Detail) - Restricted Stock Units [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Beginning Balance	220,648	311,583	320,980
Number of Shares, granted	31,900	79,300	118,864
Number of Shares, vested	(59,008)	(89,915)	(120,721)
Number of Shares, cancelled/forfeited/expired	(68,300)	(80,320)	(7,540)
Number of Shares, Ending Balance	125,240	220,648	311,583
Weighted-Average Grant Date Fair Value, Beginning Balance	$ 30.70	$ 29.78	$ 28.47
Weighted-Average Grant Date Fair Value, granted	25.75	31.86	30.85
Weighted-Average Grant Date Fair Value, vested	29.69	27.97	27.30
Weighted-Average Grant Date Fair Value, cancelled/forfeited/expired	29.33	31.35	30.34
Weighted-Average Grant Date Fair Value, Ending Balance	$ 30.66	$ 30.70	$ 29.78
Aggregate Intrinsic Value	$ 4.9