Stockholders' Equity - Additional Information (Detail) - USD ($)		3 Months Ended		9 Months Ended
	Oct. 13, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Subsequent Event [Line Items]
Stock repurchased and retired, total costs				$ 464,000	$ 792,000
Dividends per common share		$ 0.30	$ 0.30	$ 0.90	$ 0.90
Common Stock [Member]
Subsequent Event [Line Items]
Repurchase and retirement of common stock, shares				14,934	17,493
Share Repurchase Plan [Member]
Subsequent Event [Line Items]
Stock repurchased and retired, total costs				$ 18,023,000	$ 1,610,000
Share Repurchase Plan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends per common share	$ 0.30
Date of dividend payable	Dec. 16, 2016
Record date of dividend payable	Nov. 18, 2016
Share Repurchase Plan [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Repurchase and retirement of common stock, shares				574,851	37,869
Share Repurchase Plan [Member] | 2015 Plan [Member]
Subsequent Event [Line Items]
Common stock repurchase authorized amount						$ 20,000,000
Common stock repurchased and retired, weighted average price		$ 30.29		$ 31.31
Stock repurchased and retired, total costs		$ 6,008,000		$ 18,023,000
Fees and commissions average price repurchase common stock		$ 30.33		$ 31.35
Share Repurchase Plan [Member] | 2015 Plan [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Repurchase and retirement of common stock, shares		198,055		574,851
Share Repurchase Plan [Member] | 2014 Plan [Member]
Subsequent Event [Line Items]
Common stock repurchase authorized amount							$ 40,000,000
Common stock repurchased and retired, weighted average price					$ 42.49
Stock repurchased and retired, total costs					$ 1,610,000
Fees and commissions average price repurchase common stock					$ 42.51
Time through the company is allowed to repurchase shares					Mar. 31, 2015
Share Repurchase Plan [Member] | 2014 Plan [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Repurchase and retirement of common stock, shares			0		37,869