Income taxes - Reconciliation of Income Tax Expenses Computed at Federal Statutory Rate with Income Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Expected income tax (benefit) expense at 35%	$ (194)	$ 15,140	$ 32,027
Foreign tax rate differential	(329)	(693)	(422)
State income tax (benefit) expense – net of Federal impact	(914)	(840)	1,586
Impairment of goodwill	7,099	0	0
Nondeductible expenses	2,768	4,060	2,321
Return-to-provision adjustments	(1,329)	1,133	(2,408)
Valuation allowance	(668)	(5,020)	(6,555)
Intercompany dividends and dividends received deductions	(541)	(319)	449
Tax-exempt interest	(404)	(324)	(233)
Noncontrolling interest	251	186	529
Life insurance proceeds	(175)	0	(797)
Nondeductible bond conversion costs	0	0	1,900
Other – net	86	180	84
Income tax expense	$ 5,650	$ 13,503	$ 28,481
Effective income tax rates	(1019.40%)	31.20%	31.10%