Income Taxes Changes in Unrecognized Tax Benefit (Including Interest and Penalties) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 8,900
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	5,711	$ 3,658	$ 3,497
Additions for tax positions for current year	3,141	793	1,208
Additions for tax positions for prior years	4,132	1,593	228
Lapse of the applicable statute of limitations	(77)	(46)	(25)
Reduction for tax positions for prior years	(224)	(287)	(1,250)
Ending Balance	12,683	5,711	3,658
Unrecognized Tax Benefits Before Interest And Penalties
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	5,269	3,357	3,397
Additions for tax positions for current year	3,141	793	1,208
Additions for tax positions for prior years	3,378	1,427	0
Lapse of the applicable statute of limitations	(60)	(37)	(20)
Reduction for tax positions for prior years	(223)	(271)	(1,228)
Ending Balance	11,505	5,269	3,357
Interest & Penalties
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	442	301	100
Additions for tax positions for current year	0	0	0
Additions for tax positions for prior years	754	166	228
Lapse of the applicable statute of limitations	(17)	(9)	(5)
Reduction for tax positions for prior years	(1)	(16)	(22)
Ending Balance	$ 1,178	$ 442	$ 301