Stock-Based Compensation - Time-Based Restricted Stock Activity (Detail) - Time-Based Restricted Stock [Member] - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Restricted Stock Activity [Line Items]
Nonvested, Shares, Beginning Balance	107,907	329,562	382,974
Time-based Restricted Stock, Granted	57,874	57,598	66,511
Time-based Restricted Stock, Vested	(43,848)	(230,704)	(116,641)
Time-based Restricted Stock, Forfeited	(133)	(48,549)	(3,282)
Nonvested, Shares, Ending Balance	121,800	107,907	329,562
Nonvested, Weighted-Average Grant Price Per Share, Beginning Balance	$ 29.43	$ 18.89	$ 13.78
Weighted-Average Grant Price Per Share, Granted	37.64	43.81	32.70
Weighted-Average Grant Price Per Share, Vested	42.34	42.37	33.73
Weighted-Average Grant Price Per Share, Forfeited	43.89	20.20	16.61
Nonvested, Weighted-Average Grant Price Per Share, Ending Balance	$ 31.59	$ 29.43	$ 18.89