Income Taxes - Activity of Valuation Allowance for Deferred Tax Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation Allowance
Valuation allowance at beginning of year	$ 131,985	$ 113,051	$ 82,125
Increase in valuation allowance as a result of mergers and acquisitions, net	914	1,930	0
Increase in valuation allowance as a result of current year operations	28,761	17,004	30,926
Valuation allowance at end of year	$ 161,660	$ 131,985	$ 113,051