Stock Buy Back Plans - Additional Information (Detail) - USD ($)	1 Months Ended							12 Months Ended
	Aug. 31, 2016	Jul. 31, 2016	Jun. 30, 2016	May 31, 2016	Apr. 30, 2016	Mar. 31, 2016	Feb. 28, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Feb. 02, 2016
Equity Class Of Treasury Stock [Line Items]
Purchase of treasury shares (in shares)	299,931	66,422	330,265	307,798	454,729	269,099	943,983	2,672,227
Purchase of treasury shares								$ 100,000,000	$ 28,823,000	$ 18,024,000
Class A Common Stock [Member]
Equity Class Of Treasury Stock [Line Items]
Stock repurchase program, authorized amount											$ 100,000,000
Purchase of treasury shares (in shares)								2,672,227
Class A Common Stock [Member] | Employee Restricted Stock Plan [Member]
Equity Class Of Treasury Stock [Line Items]
Stock tendered for payments of withholding taxes (in shares)								73,546	77,732
Purchase of treasury shares								$ 2,500,000	$ 2,900,000