Operating Segment and Enterprise Wide Reporting - Schedule of Revenues by Geographic Destination and as a Percentage of Total Revenues (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue	$ 83,446	$ 77,427	$ 87,821	$ 77,401	$ 80,975	$ 74,753	$ 82,811	$ 75,187	$ 326,095	$ 313,726	$ 312,062
Revenues by geographical area percentage									100.00%	100.00%	100.00%
United States [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue									$ 252,222	$ 241,025	$ 232,440
Revenues by geographical area percentage									77.00%	77.00%	74.00%
Europe (Excluding United Kingdom) [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue									$ 27,061	$ 24,607	$ 30,257
Revenues by geographical area percentage									8.00%	8.00%	10.00%
United Kingdom [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue									$ 14,808	$ 16,815	$ 16,804
Revenues by geographical area percentage									5.00%	5.00%	5.00%
Canada [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue									$ 13,806	$ 14,424	$ 17,089
Revenues by geographical area percentage									4.00%	5.00%	6.00%
Other [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenue									$ 18,198	$ 16,855	$ 15,472
Revenues by geographical area percentage									6.00%	5.00%	5.00%