Schedule of Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total assets	$ 1,670,941	$ 1,360,259
Goodwill	348,661	262,376	$ 262,594
Hub [Member]
Segment Reporting Information [Line Items]
Goodwill	319,272	232,987	$ 233,205
Operating Segments [Member] | Hub [Member]
Segment Reporting Information [Line Items]
Total assets	1,470,792	1,178,110
Goodwill	319,272	232,987
Operating Segments [Member] | Mode LLC [Member]
Segment Reporting Information [Line Items]
Total assets	210,088	191,374
Goodwill	29,389	29,389
Intersegment Elims [Member]
Segment Reporting Information [Line Items]
Total assets	$ (9,939)	$ (9,225)