Stockholders' Equity - Additional Information (Detail) - USD ($)		3 Months Ended		6 Months Ended
	Jul. 08, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Subsequent Event [Line Items]
Stock repurchased and retired, total costs				$ 447,000	$ 772,000
Dividends per common share		$ 0.30	$ 0.30	$ 0.60	$ 0.60
Common Stock [Member]
Subsequent Event [Line Items]
Repurchase and retirement of common stock, shares				14,400	16,958
Share Repurchase Plan [Member]
Subsequent Event [Line Items]
Stock repurchased and retired, total costs				$ 12,015,000	$ 1,610,000
Share Repurchase Plan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends per common share	$ 0.30
Date of dividend payable	Sep. 16, 2016
Record date of dividend payable	Aug. 19, 2016
Share Repurchase Plan [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Repurchase and retirement of common stock, shares				376,796	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		$ 31.59		$ 31.85
Stock repurchased and retired, total costs		$ 6,008,000		$ 12,015,000
Fees and commissions average price repurchase common stock		$ 31.63		$ 31.89
Share Repurchase Plan [Member] | 2015 Plan [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Repurchase and retirement of common stock, shares		189,938		376,796
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