Segment information - Selected Statement of Operations and Income (Loss) Information Related to Segments (Detail) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
	Feb. 10, 2016	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
Segment Reporting Information [Line Items]
Revenues		$ 525,764	$ 553,210	$ 489,437	$ 438,229	$ 497,403	$ 555,705	$ 531,906	$ 448,871	$ 2,006,640	$ 2,033,885	$ 1,870,830
Impairment of goodwill	$ 35,900									0	35,749	0
Depreciation and amortization										30,044	30,298	24,226
Income (loss) before taxes and noncontrolling interest										88,026	9,693	51,812
Title
Segment Reporting Information [Line Items]
Revenues										1,922,422	1,904,258	1,730,875
Impairment of goodwill										0	1,569	0
Depreciation and amortization										21,176	18,767	16,677
Income (loss) before taxes and noncontrolling interest										139,083	119,032	90,786
Ancillary Services and Corporate
Segment Reporting Information [Line Items]
Revenues										84,218	129,627	139,955
Impairment of goodwill										0	34,180	0
Depreciation and amortization										8,868	11,531	7,549
Income (loss) before taxes and noncontrolling interest										$ (51,057)	$ (109,339)	$ (38,974)