Employee Stock Purchase Plan (Detail)	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESPP Shares Issued	3,039,200
Prior To Two Thousand Fourteen [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESPP Shares Issued	2,899,528
Price per ESPP Share Issued | $ / shares	$ 13.78
January 1 2015 To March 31 2015 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESPP Shares Issued	24,368
Price per ESPP Share Issued | $ / shares	$ 22.76
April 1 2015 To June 30 2015 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESPP Shares Issued	15,750
Price per ESPP Share Issued | $ / shares	$ 33.77
July 1 2015 To September 30 2015 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESPP Shares Issued	18,984
Price per ESPP Share Issued | $ / shares	$ 32.27
October 1 2015 To December 31 2015 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESPP Shares Issued	19,082
Price per ESPP Share Issued | $ / shares	$ 33.42
January 1 2016 To March 31 2016 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESPP Shares Issued	13,850
Price per ESPP Share Issued | $ / shares	$ 41.09
April 1 2016 To June 30 2016 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESPP Shares Issued	14,236
Price per ESPP Share Issued | $ / shares	$ 42.91
July 1 2016 To September 30 2016 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESPP Shares Issued	16,520
Price per ESPP Share Issued | $ / shares	$ 40.32
October 1 2016 To December 31 2016 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
ESPP Shares Issued	16,882
Price per ESPP Share Issued | $ / shares	$ 36.24